Journal of Neuroimmunology, 40 (1992) 225-230
225
,~ 1992 Elsevier Science Publishers B.V. All rights reserved 0165-5728/92/$05.00 JNI 90011
Multiple sclerosis and vitamin B12 metabolism E.H. R e y n o l d s Maudsley and Kings College Hospitals, London, UK
Key words: Multiple sclerosis; Vitamin B12 deficiency
Summary Multiple sclerosis (MS) is occasionally associated with vitamin B12 deficiency. Recent studies have shown an increased risk of macrocytosis, low serum a n d / o r CSF vitamin B12 levels, raised plasma homocysteine and raised unsaturated R-binder capacity in MS. The aetiology of the vitamin B12 deficiency in MS is often uncertain and a disorder of vitamin B12 binding or transport is suspected. The nature of the association of vitamin B12 deficiency and MS is unclear but is likely to be more than coincidental. There is a remarkable similarity in the epidemiology of MS and pernicious anaemia. Vitamin B12 deficiency should always be looked for in MS. The deficiency may aggravate MS or impair recovery. There is evidence that vitamin B12 is important for myelin synthesis and integrity but further basic studies are required.
Introduction
Association of MS and vitamin B12 deficiency
Although multiple sclerosis (MS) is widely regarded as an inflammatory disorder of viral/ immunological aetiology, this would not exclude an important role for metabolic events in the demyelinating and remyelinating process, nor indeed that there may be a sub-group of patients in whom metabolic factors may play a primary role. In this paper, the possible significance of vitamin B12 metabolism will be discussed in MS and other disorders in which demyelination occurs. This was a topic of interest briefly in the late 1950s and early 1960s, but has been revived by recent clinical observations.
Over a period of 5 years in the early 1980s, three patients were observed with MS and unusual vitamin B12 deficiencies (Reynolds and Linnell, 1987). Following presentation of these three cases to the Association of British Neurologists (Reynolds and Linnell, 1988), seven further examples were referred. These ten cases have recently been described (Reynolds et al., 1991). The age of presentation of the neurological disorder was typical of MS and there was little doubt about the diagnosis, which had already been made by other neurologists in seven cases prior to referral. Surprisingly, none of the patients had the classical neurological features of vitamin B12 deficiency. In particular, none had clinical or electromyographic evidence of peripheral nerve involvement although peripheral neuropathy is the most common modern neurological
Correspondence to: E.H. Reynolds, Department of Neurology, King's College Hospital, Denmark Hill, London SE5 9RS, UK.
22~ manifestation of vitamin B 12 deficiency (Shorvon et al., 1980). The vitamin BI2 deficiency was detected at the onset of the neurological disorder in nine of the cases. The exception was a young man who at the age of 27 years presented with megaloblastic anaemia due to juvenile pernicious anaemia. He had mild sensoD, symptoms (but no signs) which resolved on treatment and he remained well on vitamin B12 therapy until he presented at the age of 39 with MS (Reynolds et al., 1991. Case 1: see also Linnell et al., 1981). There were several unusual features about the haematological findings in this series of patients, including the fact that vitamin BI2 deficiency is rare in the young adult age range, occurring in less than 10% below the age of 4(1 years (Chanarin, 1979). The deficiency was confirmed in most patients by macrocytosis, megaloblastic marrow a n d / o r low red cell cobalamin (vitamin B12), in addition to the usual low serum vitamin B12, but only two patients were anaemic, in one of whom an associated iron-deficiency played a role. However, the explanation for the vitamin B12 deficiency was uncertain in most of our patients, only two, possibly three, of the ten having pernicious anaemia. No patient had gastrointestinal disease and in the absence of any other explanation, a disorder of vitamin BI2 binding or transport was suspected, especially as a few of our patients (including case 1) exhibited continuing macrocytosis despite treatment with vitamin BI2. The coexistence of MS and vitamin BI2 deficiency in these patients is intriguing and on the basis of epidemiological and other considerations to be discussed later, is likely to be more than coincidental (Reynolds et al., 1991). These observations have prompted further studies of vitamin B12 metabolism in MS.
Studies of vitamin B12 metabolism in MS
Macrocytosis Retrospective review of the blood counts on all patients with definite MS admitted to King's College Hospital in one year was conducted. The haemoglobin and mean cell volume (MCV) were compared in 27 patients with MS and an age- and
sex-matched control group of neurological patients admitted to the same ward (Crellin et al., 199(/). Although the haemoglobin was identical in the two groups, patients with MS were mildly but significantly macrocytic, with most values in the top half of the reference range. These observations have been confirmed in a larger study by Najim AI-Din et al. (1991). Neither study could explain the macrocyto,sis as vitamin B12 and folate assays are not routinely undertaken in MS. However, it seems unlikely that the macrocytosis was entirely the result of chronic disease for nutritional or other reasons, as in the study of Najim AI-Din et al. (1991), the macrocytosis was often detected at the onset of the disorder. These two recent studies are in keeping with earlier reports of slight increase in red cell size in MS by Plum and Fog (1959) and Prineas (1968).
FTtamin BI2 lecels Serum. An unselected prospective series of patients with MS attending the neurology department at King's College Hospital had significantly lower serum vitamin B12 levels than neurological and normal control groups (Reynolds eta[., 1992). Nine of 29 patients with MS had serum vitamin B12 levels below 200 p g / m l and this subgroup was significantly macrocytic and had significant lowering of red cell folate, as is known to occur in vitamin B12 deficiency. Between 1957 and 1965. there were several studies of serum vitamin BI2 in MS (Bauer and Heinrich, 1957: O ' C o n n o r et al., 1960, Grann and Glass, 1961, Gjertsen and Schrumpf, 1962; Worm-Peterson, 1962; Simpson. 1964, Basil et al., 1965), because of interest in a possible role for vitamin B12 in myelin formation. Some of the earlier studies reported that serum vitamin BI2 levels were low (Bauer and Heinrich, 1957; O ' C o n n o r et al., 1960; Gjertsen and Schrumpf, 1962), but some later studies were "negative" (Grann and Glass, 1961: Worm-Peterson, 1962; Simpson, 1964, Basil et a[., 1965). It is interesting in retrospect that six of Simpson's (1964) 46 patients clearly had low serum vitamin B12 levels (64-118 p g / m l ) which was not seen in the control group.
Cerebro~pinal ]luid (CSF). A few studies of CSF vitamin B12 in MS between 1962 and 1965 (Gjertsen and Schrumpf, 1962; Worm-Petersen,
227 1962; Simpson, 1964; Basil et al., 1965) produced conflicting findings, although there was a tendency for CSF vitamin B12 to be lower. However, there is very little vitamin B12 detectable in normal CSF and routine assay procedures suitable for the large quantities of the vitamin present in serum are not usually sensitive enough to detect CSF vitamin B12 changes in disease. Employing a new more sensitive technique, Njist et al. (1990) have recently reported significant lowering of CSF vitamin B12 in MS. Although the fall in serum vitamin B12 in this group of patients was not significant, there was a significant correlation between serum and CSF values. However, some individuals may have a low CSF vitamin B12 and normal serum vitamin B12. Vitamin B12 binders As already noted, a disorder of vitamin BI2 binding or transport was suspected in some of the patients with MS and vitamin B12 deficiency (Reynolds et al., 1991). In these systematic studies of vitamin BI2 metabolism in MS, measurements were included of unsaturated plasma transcobalamin 11 (TC11)-binding capacity as well as unsaturated R-binding capacity. All body fluids, including plasma, contain a Cbl-binding glycoprotein which on electrophoresis moves more rapidly than T C l l , hence the name rapid or R-binder. No significant changes in T C l l were found, but significant elevation of the R-binder capacity was seen, in a few patients to very high levels (Reynolds et al., 1992). The unsaturated R-binder was highly correlated with serum vitamin B12 in control subjects but not in MS patients. The function of R-binder is unknown, but it is interesting that there are three case reports in the literature of a possible association between MS and R-binder deficiency (Carmel and Herbert, 1969; Sigal et al., 1987). The author is unaware of any report of neurological disease associated with excess R-binder. Homocysteine Until very recently, the diagnosis of vitamin B12 deficiency has been very dependent on the serum vitamin B12 assay. However, there is some evidence that the serum vitamin B12 level is not an entirely reliable guide to tissue vitamin B12
deficiency and some uncertainty exists as to the level at which a confident diagnosis of deficiency can be made. New evidence suggests that plasma homocysteine may be a useful guide to functional vitamin B12 deficiency (Allen et al., 1990). Homocysteine is normally converted to methionine by accepting a methyl group from methylfolate in a reaction mediated by the enzyme, methionine synthetase, which requires vitamin B12 (in the form of methyl cobalamin) as a co-factor. In the presence of either vitamin BI2 or folate deficiency, plasma homocysteine levels rise. In the present systematic studies of vitamin B12 metabolism in MS, plasma homocysteine determinations were included. In a population of outpatients with MS, plasma homocysteine levels were significantly elevated and negatively correlated with serum vitamin B12 levels, suggesting that low levels of serum vitamin B12 in MS were associated with functional vitamin B12 deficiency even in the absence of overt haematological manifestations of deficiency (Bottiglieri, Laundy, Crellin, Kirker and Reynolds, unpublished observations).
Significance of vitamin B12 deficiency in MS It is apparent from the case reports and from the studies of vitamin B12 metabolism in MS described above that there is a subgroup of patients with MS associated with vitamin BI2 deficiency or an overlap of MS and vitamin B12 deficiency. The majority of patients with MS do not have any presently detectable vitamin B12 deficiency. It is unlikely that the association of MS and vitamin B12 deficiency is coincidental. Vitamin B12 deficiency is uncommon in the MS age range and rare under the age of 40 (Chanarin, 1979). It is predominantly a disorder of middle or late life. On the basis of epidemiological and age considerations, the risk of the two disorders occurring together by chance is remote (Reynolds et al.. 1991). What is the cause o f citamin B12 deficiency in MS? One of the difficulties in evaluating the relationship between the two disorders and, at the same time, one of the many interesting aspects of
22s the association, is that in most cases the cause of the vitamin B12 deficiency is not clear. As already pointed out, only a minority of those MS patients with vitamin BI2 deficiency have pernicious anaemia on the basis of the usual criteria of a characteristically abnormal Schilling test, together with intrinsic factor antibodies. In the UK. as in most countries, pernicious anaemia is the most common cause of vitamin B12 deficiency. None of the patients we have yet studied in detail had a histo~3,' of gastrointestinal disease or dietary deficiency associated with veganism. At present, interest is focussed on disturbances in vitamin BI2 binding or transport, stimulated by observations on unsaturated R-binder capacity (Reynolds et al.. 1991, 1992). Whether the putative abnormality of vitamin BI2 binding or transport is the result of an autoimmune process, as in the case of pernicious anaemia, is also unknown, but clearly relevant to any discussion about a relationship with MS. Some of the present patients had various non-specific antibodies, others did not (Reynolds et al., 1991).
Po~wible c a u s e s B I 2 de[k'ieno'
Of an ot'erlap of MS and vitamin
One possibility is that the combined occurrence of MS and vitamin BI2 deficiency represents an increased association of two autoimmune disorders. It is remarkable that, despite the age range being so different, the sex, racial and geographical distribution of MS and pernicious anaemia are similar (Crellin et al., 1990; Reynolds et al., 1991). Thus pernicious anaemia has a higher prevalence in Northern Europe compared with Southern Europe and tropical areas, a diminishing prevalence from the north to the south of the UK and a higher incidence in Caucasian than black North Americans (Chanarin, 1979). The female-to-male ratio in both disorders is 1.3:1. Najim AI-Din et al. (1991) have also drawn attention to some similarities in the H L A associations of MS and pernicious anaemia, particularly with respect to HLA-A3, HLA-B7, H L A - D R W 2 and DR2. Two families have been studied in which a father and son, and father and daughter, both had MS and vitamin BI2 deficiency. In one family, the cause of the vitamin B12 deficiency was
pernicious anaemia, the other uncertain (Reynolds, unpublished observ'ations). Two other possible explanations for the association of the two disorders arc (1) that vitamin B12 deficiency, from whatever cause, renders some patients more vulnerable to the putative viral/immunological mechanisms widely suspected in MS (Reynolds ct al., 1991), or (2) that chronic immune reactions or recurrent myelin repair processes increase the demand for vitamin B12 (,Reynolds et al., 1992). With regard to the former, there is some evidence that isolated vitamin deficiencies, including deficiency of vitamin BI2, can impair immunological processes (Stites et al., 1t~87). With regard to the second possibility, this might explain the occurrence of low CSF vitamin BI2 levels in the presence of normal serum values. Furthermore, it is highly likely that vitamin B12 is necessary for myelin formation and integrity, which includes important methylation reactions. Experimental evidence in support of this view is derived from the cycloleucine (Crang and Jacobson, 1980) and nitrous oxide (Scott et al., 1981) models of subacute combined degeneration. Indeed, impressive evidence of a probable role for vitamin B12 in myelin formation comes from recent studies of children with inborn errors of vitamin B12 metabolism (Surtees et al., 1991). An important aspect of the neuropathology of these children is a failure of mye[ination, or even demyelination. Appropriate treatment can result in MRI evidence of myelination or remyelination. The close links between folate and vitamin B12 metabolism in methylation reactions in the nervous system also emphasise the need to explore the role of both vitamins in demyelinating disorders (Botez and Reynolds, 1979: Surtees et al., 1991). The question must to be considered whether there could be a more direct causal relationship between MS and vitamin B12 deficiency in this subgroup? On first reflection, it may seem rather unlikely that a deficiency that usually leads to various well-known progressive neurological syndromes should also cause a previously unrecognised relapsing and remitting syndrome, all the more so as there is thought to be a clear distinction between the "inflammatow" neuropathology of MS and the non-inflammatory neuropathology
229
of vitamin B12 deficiency. Before rejecting a causal hypothesis a few puzzling observations should be borne in mind: (1) In clinical practice the distinction between MS and 'subacute combined degeneration' (SCD) due to vitamin B12 deficiency occasionally leads to difficulty and uncertainty. (2) There are some interesting reports in the literature of patients in whom a diagnosis of MS has been made or suspected only for the authors to change the diagnosis to SCD following the discovery of an abnormality of vitamin B12 metabolism (Sigal et al., 1987; Carmel et al., 1988; Ransohoff et al., 1990). (3) None of the patients in the present series with MS and unequivocal vitamin B12 deficiency had the expected typical neurological manifestations of this deficiency state. In particular, none had clinical or electromyographic evidence of peripheral neuropathy (Reynolds et al., 1991; Reynolds, unpublished observations). This is the commonest neurological manifestation of vitamin B12 deficiency (see for example Shorvon et al., 1980) and its presence might have been anticipated in some cases on statistical grounds. (4) Demyelination is a prominent feature of the neuropathology of vitamin B12 deficiency in the spinal cord (SCD) and brain; and, as already noted, of inborn errors of vitamin B12 metabolism (Surtees et al., 1991). (5) Recently, a myelopathy which neuropathologically resembles SCD has been described in AIDS patients in the absence of vitamin B12 deficiency (Petito et al., 1985). It is unclear whether the mechanism is viral or metabolic. At the very least, it may be asked whether the associated vitamin B12 deficiency from any cause is aggravating the underlying MS or hindering the process of remyelination? Although some of the patients studied have seemed to do well on vitamin B12 therapy (Reynolds, unpublished data), such uncontrolled observations are notoriously unreliable in MS. Furthermore, for many years vitamin B12 injections have been used occasionally for placebo purposes in the treatment of MS. Although some patients were impressed with their apparent neurological benefit, there was no controlled support for this conviction (Simpson et al., 1967). Clearly, controlled treatment studies will
be required in patients with MS who have been separated into those with or without a disturbance of vitamin B12 metabolism. Finally, it is to be hoped that these predominantly clinical observations will stimulate further basic research on the role of vitamin BI2 and methylation in myelin formation and integrity and in demyelinating disorders. Little is known about the requirements of the central nervous system for vitamin B12, nor the forms in which it is needed or mechanisms by which it is transported across the blood-brain barrier. Such research would assist in the evaluation of the most appropriate form, dose or duration of therapy for optimum treatment of vitamin B12-related neurological disorders (Reynolds, 1976: Lazar and Carmel, 1981).
References Allen, R.H., Stabler, S.P., Savage, D.G. and Lindenbaum, J. (1990) Diagnosis of cobalamin deficiency I: Usefulness of serum methylmalonic acid and total homocysteine concentrations. Am. J. Hematol. 34, 90-98. Basil, W., Brown, J.K. and Matthews, D.M. (1965) Observations on vitamin B12 in serum and cerebrospinal fluid in multiple sclerosis, J. Clin. Pathol. 18, 317-321. Bauer, H. and Heinrich, H.C. (1957I Pathophysiologische Veraussetzungen zur therapeutischen Anwendung des Vitamin B12 bei neurologischen Erkrankungen. In: H.C. Heinrich (Ed.), Vitamin B12 und Intrinsic Factor. pp. 499-509. Ferdinand-Enke-Verlag, Stuttgart. Botez, M.I. and Reynolds, E.H. (19791 Folic Acid in Neurology, Psychiatry, and Internal Medicine. Raven Press, New York, NY. Carmel, R. and Herbert, V. (1969) Deficiency of vitamin Bl2-binding alpha globulin in two brothers. Blood 33, 1-12. Carmel, R., Watkins, D., Goodman, .S.I. and Rosenblatt, D.S. (1988) Hereditary defect of cobalamin metabolism (cblG Mutation) presenting as a neurologic disorder in adulthood. New Engl. J. Meal. 318, 1738-1741. Chanarin, I. (1979) The Megaloblastic Anaemias. Blackwell, Oxford. Crang, A.J. and Jacobson, W. (1980) A possible mouse model for subacute combined degeneration of the cord. In: C.F. Rose and P.O. Behan (Eds.), Recent Progress in Neurology. pp. 146-161. Pitman, London. Crellin, R.F., Bottiglieri, T. and Reynolds. E.H. (1990) Multiple sclerosis and macrocytosis. Acta Neurol. Scand. 81, 388-391. Gjertsen, F.A. and Schrumpf, A. (1962) B12-vitamin i spinal vaesken ved forskjellige sykdommer. Nord. Med. 67, 162.
23O Granth V. and Glass. G.B.J. (lCJbll Blood serum lcvcl> and intestinal absorption of vitatnin B I2 in multiple sclerosis. J. Lab. Clin. Mcd. 57, 562 567. Lazar, G.S. and Carmel. R. lit)S1) Cobulamin binding and uptake in vitro in the humatl central net",'ous system. J. Lab. Clin. Med. 07. 123-133. Linnell, J.('.. Quadros. E.V., Enghmd, J.M., Dox~n. M.C. and Reynolds+ E H . (1981) Abnot'nlal cobalamin metabolism in a case of juvenile pernicious anaemia x~ith neutoh)gical svmptoms. J. Inherited Metab. Dis. 4, 14tJ 150. Najim :\l-Din. A.S.. Khojali, M.. Habbtlsh, H., Farah, S., Idris, A.R. and AI-Muhtasib, F. t l?gl) Macrocytosis in multiple sclerosis: a study in 82 Uc *t+,+{, arab patients. J. Neurol. Neurosurg. P~,vchiat. 54, 415 4lb. Njist+ T.Q., ttommes, O.R., Weaxers, R.A., Schoonder-Waldt. H.C. and DeHaan. A.F.J. (19tJtl) X,'itamin BI2 and folate lexels of serum and cerebrospinal fluid in multiple ~,clerosis and other neurological disl+rdet's. J. Neural. Neurosurg. PsychiatiT 53, 951-c)54. O C o n n o r , J.S., Dart,,,, R.L., kang+~orth}. O.R. and Chow, B.F. (191-,(I) B12 nletaholism and mnltiplc sclcrosi,',. Proc. Soc. Exp. Biol. Med. 1(13. 180 183. Petit\l, C.K.. Navia. B.A., Cho, E.-S., Jt)rcialh B.D., George. I).('. and Price, R.W. (ltJ85) Vacuolar m velopathy palhoIogicall.,< resembling subacute combincd degeneration in patients ~ith ttlc acquired immunodeficicnc.x syndrome. New Engl. J. Med. 312, 87-I S70. Plum, C.M. and Fog. T. (1959) Studics in multiple sclerosis. Acia Psychiatr. Neurol. Scand. (Suppl.128)34, 13-18. Prineas, J. (IC)e,SI Red blood cell size in multiple sclero,,,i~. Acta Neurol. Scand. 44, gl-91). Ransohoff, R.M.. Jacobsen. D.W. and Green, R. (19cJ()) Vitamin BI2 deficiency and multiple sclerosis. Lancet 335. 1285-128h.Reynolds, IE.H. (197b) Neurology of vitamin B I2 deficienc$. Lancet ii, 832 833. Reynolds, E.H. and Linnell, J.('. (It)87) Vitamin BI2 deft
clench, dcmxclination and muhiplc ,,cleric,d,,.[,ancct il. Y!(I. Reynuld,~. E.II. and Linncll. J.('. flu\X) Muhiplc sclerosis und vitamin B 12 metabolism: a ne~ clue..I. Ncurot. Ncurosurg. P>ychiatr_~ 5 l, 73Y. Resnold~. E.H.. LinncII, J.(. and Faludv. ].E. (1991) MultipI~: sclerosis us~,ociatcd with vitamin BI2 dclicienc'$. Arch. Ncnro]. 4~, HII,~-~I I. Rcynolds, E l l . , Bottiglicri, I . . Laund$. I%.I.. Crellin. R.F. and Kirker, S.G. (1t;92) Vitamin BI2 metabolism in multiplc sclerosi,,. Arch. Ncurol.. in pres~,. Scott, J.M., Dinn, J.. \Vils~m. P. and Weir, D.G. ( 1~811 Pathogenesis of ,,ubacutc combined dcgcTlcratioll: A result t~l meth.~l group d¢liciency. Lancet it, 334 337. Shc,tworl, S.D., ('arnc,,, M.W.P.. Chanarin. I. and Re.vnolds, E.H. { It)81l) The ncuropsychiatry of megaloblastic an~lemki. Bt. Mcd. ,1. 281, 11131">-11)3X. Sigal. S.H.. Hull, ('.A. and Anle], J.P. (ltJ8 "7) Plasma R-bindci dcficicnc>, and ncurologic disease. Nex~ Engl. J. Mcd. 317. 1331)- 1332. Simpson. ('.,\. (1964) Vitamin BI2 levels in the ~,crtlnl :.illd cerebrospinal fluid in rnuhiple sclerosis. J. Ncurol. Neurosurg. Psychialr_,, 27. 174 177. Simpson, ('.A.. Newell, D.J. and Miller, tl. (lY671 [he treatment ol multiple sclerosi,,, ~ith massive doses ot h!,'droxucobalamin. Neut'olog.~ 15. 5t) t) hi13. Stites. D.P., Stobo, J.I)., Fudctl.berg. tI.H. and Well>, ,I.\'. (iris7) I=Jasic anti Clinical Imnuinolt~g_~. hth Edn.. l_angc Medical Publicatiun,,. l,os Altos, ('A. Surtccs. i . , Leonard, J. and Austin, S. (ItJqll Association ~*1 dcm$,elination ~ith deficiency tit ccrebrospinal-fhlid sadenos).hnethionine in inborn errors t)f melh_,,I-tran,',fer paihwu$. Lancet 338, 155
225
,~ 1992 Elsevier Science Publishers B.V. All rights reserved 0165-5728/92/$05.00 JNI 90011
Multiple sclerosis and vitamin B12 metabolism E.H. R e y n o l d s Maudsley and Kings College Hospitals, London, UK
Key words: Multiple sclerosis; Vitamin B12 deficiency
Summary Multiple sclerosis (MS) is occasionally associated with vitamin B12 deficiency. Recent studies have shown an increased risk of macrocytosis, low serum a n d / o r CSF vitamin B12 levels, raised plasma homocysteine and raised unsaturated R-binder capacity in MS. The aetiology of the vitamin B12 deficiency in MS is often uncertain and a disorder of vitamin B12 binding or transport is suspected. The nature of the association of vitamin B12 deficiency and MS is unclear but is likely to be more than coincidental. There is a remarkable similarity in the epidemiology of MS and pernicious anaemia. Vitamin B12 deficiency should always be looked for in MS. The deficiency may aggravate MS or impair recovery. There is evidence that vitamin B12 is important for myelin synthesis and integrity but further basic studies are required.
Introduction
Association of MS and vitamin B12 deficiency
Although multiple sclerosis (MS) is widely regarded as an inflammatory disorder of viral/ immunological aetiology, this would not exclude an important role for metabolic events in the demyelinating and remyelinating process, nor indeed that there may be a sub-group of patients in whom metabolic factors may play a primary role. In this paper, the possible significance of vitamin B12 metabolism will be discussed in MS and other disorders in which demyelination occurs. This was a topic of interest briefly in the late 1950s and early 1960s, but has been revived by recent clinical observations.
Over a period of 5 years in the early 1980s, three patients were observed with MS and unusual vitamin B12 deficiencies (Reynolds and Linnell, 1987). Following presentation of these three cases to the Association of British Neurologists (Reynolds and Linnell, 1988), seven further examples were referred. These ten cases have recently been described (Reynolds et al., 1991). The age of presentation of the neurological disorder was typical of MS and there was little doubt about the diagnosis, which had already been made by other neurologists in seven cases prior to referral. Surprisingly, none of the patients had the classical neurological features of vitamin B12 deficiency. In particular, none had clinical or electromyographic evidence of peripheral nerve involvement although peripheral neuropathy is the most common modern neurological
Correspondence to: E.H. Reynolds, Department of Neurology, King's College Hospital, Denmark Hill, London SE5 9RS, UK.
22~ manifestation of vitamin B 12 deficiency (Shorvon et al., 1980). The vitamin BI2 deficiency was detected at the onset of the neurological disorder in nine of the cases. The exception was a young man who at the age of 27 years presented with megaloblastic anaemia due to juvenile pernicious anaemia. He had mild sensoD, symptoms (but no signs) which resolved on treatment and he remained well on vitamin B12 therapy until he presented at the age of 39 with MS (Reynolds et al., 1991. Case 1: see also Linnell et al., 1981). There were several unusual features about the haematological findings in this series of patients, including the fact that vitamin BI2 deficiency is rare in the young adult age range, occurring in less than 10% below the age of 4(1 years (Chanarin, 1979). The deficiency was confirmed in most patients by macrocytosis, megaloblastic marrow a n d / o r low red cell cobalamin (vitamin B12), in addition to the usual low serum vitamin B12, but only two patients were anaemic, in one of whom an associated iron-deficiency played a role. However, the explanation for the vitamin B12 deficiency was uncertain in most of our patients, only two, possibly three, of the ten having pernicious anaemia. No patient had gastrointestinal disease and in the absence of any other explanation, a disorder of vitamin BI2 binding or transport was suspected, especially as a few of our patients (including case 1) exhibited continuing macrocytosis despite treatment with vitamin BI2. The coexistence of MS and vitamin BI2 deficiency in these patients is intriguing and on the basis of epidemiological and other considerations to be discussed later, is likely to be more than coincidental (Reynolds et al., 1991). These observations have prompted further studies of vitamin B12 metabolism in MS.
Studies of vitamin B12 metabolism in MS
Macrocytosis Retrospective review of the blood counts on all patients with definite MS admitted to King's College Hospital in one year was conducted. The haemoglobin and mean cell volume (MCV) were compared in 27 patients with MS and an age- and
sex-matched control group of neurological patients admitted to the same ward (Crellin et al., 199(/). Although the haemoglobin was identical in the two groups, patients with MS were mildly but significantly macrocytic, with most values in the top half of the reference range. These observations have been confirmed in a larger study by Najim AI-Din et al. (1991). Neither study could explain the macrocyto,sis as vitamin B12 and folate assays are not routinely undertaken in MS. However, it seems unlikely that the macrocytosis was entirely the result of chronic disease for nutritional or other reasons, as in the study of Najim AI-Din et al. (1991), the macrocytosis was often detected at the onset of the disorder. These two recent studies are in keeping with earlier reports of slight increase in red cell size in MS by Plum and Fog (1959) and Prineas (1968).
FTtamin BI2 lecels Serum. An unselected prospective series of patients with MS attending the neurology department at King's College Hospital had significantly lower serum vitamin B12 levels than neurological and normal control groups (Reynolds eta[., 1992). Nine of 29 patients with MS had serum vitamin B12 levels below 200 p g / m l and this subgroup was significantly macrocytic and had significant lowering of red cell folate, as is known to occur in vitamin B12 deficiency. Between 1957 and 1965. there were several studies of serum vitamin BI2 in MS (Bauer and Heinrich, 1957: O ' C o n n o r et al., 1960, Grann and Glass, 1961, Gjertsen and Schrumpf, 1962; Worm-Peterson, 1962; Simpson. 1964, Basil et al., 1965), because of interest in a possible role for vitamin B12 in myelin formation. Some of the earlier studies reported that serum vitamin BI2 levels were low (Bauer and Heinrich, 1957; O ' C o n n o r et al., 1960; Gjertsen and Schrumpf, 1962), but some later studies were "negative" (Grann and Glass, 1961: Worm-Peterson, 1962; Simpson, 1964, Basil et a[., 1965). It is interesting in retrospect that six of Simpson's (1964) 46 patients clearly had low serum vitamin B12 levels (64-118 p g / m l ) which was not seen in the control group.
Cerebro~pinal ]luid (CSF). A few studies of CSF vitamin B12 in MS between 1962 and 1965 (Gjertsen and Schrumpf, 1962; Worm-Petersen,
227 1962; Simpson, 1964; Basil et al., 1965) produced conflicting findings, although there was a tendency for CSF vitamin B12 to be lower. However, there is very little vitamin B12 detectable in normal CSF and routine assay procedures suitable for the large quantities of the vitamin present in serum are not usually sensitive enough to detect CSF vitamin B12 changes in disease. Employing a new more sensitive technique, Njist et al. (1990) have recently reported significant lowering of CSF vitamin B12 in MS. Although the fall in serum vitamin B12 in this group of patients was not significant, there was a significant correlation between serum and CSF values. However, some individuals may have a low CSF vitamin B12 and normal serum vitamin B12. Vitamin B12 binders As already noted, a disorder of vitamin BI2 binding or transport was suspected in some of the patients with MS and vitamin B12 deficiency (Reynolds et al., 1991). In these systematic studies of vitamin BI2 metabolism in MS, measurements were included of unsaturated plasma transcobalamin 11 (TC11)-binding capacity as well as unsaturated R-binding capacity. All body fluids, including plasma, contain a Cbl-binding glycoprotein which on electrophoresis moves more rapidly than T C l l , hence the name rapid or R-binder. No significant changes in T C l l were found, but significant elevation of the R-binder capacity was seen, in a few patients to very high levels (Reynolds et al., 1992). The unsaturated R-binder was highly correlated with serum vitamin B12 in control subjects but not in MS patients. The function of R-binder is unknown, but it is interesting that there are three case reports in the literature of a possible association between MS and R-binder deficiency (Carmel and Herbert, 1969; Sigal et al., 1987). The author is unaware of any report of neurological disease associated with excess R-binder. Homocysteine Until very recently, the diagnosis of vitamin B12 deficiency has been very dependent on the serum vitamin B12 assay. However, there is some evidence that the serum vitamin B12 level is not an entirely reliable guide to tissue vitamin B12
deficiency and some uncertainty exists as to the level at which a confident diagnosis of deficiency can be made. New evidence suggests that plasma homocysteine may be a useful guide to functional vitamin B12 deficiency (Allen et al., 1990). Homocysteine is normally converted to methionine by accepting a methyl group from methylfolate in a reaction mediated by the enzyme, methionine synthetase, which requires vitamin B12 (in the form of methyl cobalamin) as a co-factor. In the presence of either vitamin BI2 or folate deficiency, plasma homocysteine levels rise. In the present systematic studies of vitamin B12 metabolism in MS, plasma homocysteine determinations were included. In a population of outpatients with MS, plasma homocysteine levels were significantly elevated and negatively correlated with serum vitamin B12 levels, suggesting that low levels of serum vitamin B12 in MS were associated with functional vitamin B12 deficiency even in the absence of overt haematological manifestations of deficiency (Bottiglieri, Laundy, Crellin, Kirker and Reynolds, unpublished observations).
Significance of vitamin B12 deficiency in MS It is apparent from the case reports and from the studies of vitamin B12 metabolism in MS described above that there is a subgroup of patients with MS associated with vitamin BI2 deficiency or an overlap of MS and vitamin B12 deficiency. The majority of patients with MS do not have any presently detectable vitamin B12 deficiency. It is unlikely that the association of MS and vitamin B12 deficiency is coincidental. Vitamin B12 deficiency is uncommon in the MS age range and rare under the age of 40 (Chanarin, 1979). It is predominantly a disorder of middle or late life. On the basis of epidemiological and age considerations, the risk of the two disorders occurring together by chance is remote (Reynolds et al.. 1991). What is the cause o f citamin B12 deficiency in MS? One of the difficulties in evaluating the relationship between the two disorders and, at the same time, one of the many interesting aspects of
22s the association, is that in most cases the cause of the vitamin B12 deficiency is not clear. As already pointed out, only a minority of those MS patients with vitamin BI2 deficiency have pernicious anaemia on the basis of the usual criteria of a characteristically abnormal Schilling test, together with intrinsic factor antibodies. In the UK. as in most countries, pernicious anaemia is the most common cause of vitamin B12 deficiency. None of the patients we have yet studied in detail had a histo~3,' of gastrointestinal disease or dietary deficiency associated with veganism. At present, interest is focussed on disturbances in vitamin BI2 binding or transport, stimulated by observations on unsaturated R-binder capacity (Reynolds et al.. 1991, 1992). Whether the putative abnormality of vitamin BI2 binding or transport is the result of an autoimmune process, as in the case of pernicious anaemia, is also unknown, but clearly relevant to any discussion about a relationship with MS. Some of the present patients had various non-specific antibodies, others did not (Reynolds et al., 1991).
Po~wible c a u s e s B I 2 de[k'ieno'
Of an ot'erlap of MS and vitamin
One possibility is that the combined occurrence of MS and vitamin BI2 deficiency represents an increased association of two autoimmune disorders. It is remarkable that, despite the age range being so different, the sex, racial and geographical distribution of MS and pernicious anaemia are similar (Crellin et al., 1990; Reynolds et al., 1991). Thus pernicious anaemia has a higher prevalence in Northern Europe compared with Southern Europe and tropical areas, a diminishing prevalence from the north to the south of the UK and a higher incidence in Caucasian than black North Americans (Chanarin, 1979). The female-to-male ratio in both disorders is 1.3:1. Najim AI-Din et al. (1991) have also drawn attention to some similarities in the H L A associations of MS and pernicious anaemia, particularly with respect to HLA-A3, HLA-B7, H L A - D R W 2 and DR2. Two families have been studied in which a father and son, and father and daughter, both had MS and vitamin BI2 deficiency. In one family, the cause of the vitamin B12 deficiency was
pernicious anaemia, the other uncertain (Reynolds, unpublished observ'ations). Two other possible explanations for the association of the two disorders arc (1) that vitamin B12 deficiency, from whatever cause, renders some patients more vulnerable to the putative viral/immunological mechanisms widely suspected in MS (Reynolds ct al., 1991), or (2) that chronic immune reactions or recurrent myelin repair processes increase the demand for vitamin B12 (,Reynolds et al., 1992). With regard to the former, there is some evidence that isolated vitamin deficiencies, including deficiency of vitamin BI2, can impair immunological processes (Stites et al., 1t~87). With regard to the second possibility, this might explain the occurrence of low CSF vitamin BI2 levels in the presence of normal serum values. Furthermore, it is highly likely that vitamin B12 is necessary for myelin formation and integrity, which includes important methylation reactions. Experimental evidence in support of this view is derived from the cycloleucine (Crang and Jacobson, 1980) and nitrous oxide (Scott et al., 1981) models of subacute combined degeneration. Indeed, impressive evidence of a probable role for vitamin B12 in myelin formation comes from recent studies of children with inborn errors of vitamin B12 metabolism (Surtees et al., 1991). An important aspect of the neuropathology of these children is a failure of mye[ination, or even demyelination. Appropriate treatment can result in MRI evidence of myelination or remyelination. The close links between folate and vitamin B12 metabolism in methylation reactions in the nervous system also emphasise the need to explore the role of both vitamins in demyelinating disorders (Botez and Reynolds, 1979: Surtees et al., 1991). The question must to be considered whether there could be a more direct causal relationship between MS and vitamin B12 deficiency in this subgroup? On first reflection, it may seem rather unlikely that a deficiency that usually leads to various well-known progressive neurological syndromes should also cause a previously unrecognised relapsing and remitting syndrome, all the more so as there is thought to be a clear distinction between the "inflammatow" neuropathology of MS and the non-inflammatory neuropathology
229
of vitamin B12 deficiency. Before rejecting a causal hypothesis a few puzzling observations should be borne in mind: (1) In clinical practice the distinction between MS and 'subacute combined degeneration' (SCD) due to vitamin B12 deficiency occasionally leads to difficulty and uncertainty. (2) There are some interesting reports in the literature of patients in whom a diagnosis of MS has been made or suspected only for the authors to change the diagnosis to SCD following the discovery of an abnormality of vitamin B12 metabolism (Sigal et al., 1987; Carmel et al., 1988; Ransohoff et al., 1990). (3) None of the patients in the present series with MS and unequivocal vitamin B12 deficiency had the expected typical neurological manifestations of this deficiency state. In particular, none had clinical or electromyographic evidence of peripheral neuropathy (Reynolds et al., 1991; Reynolds, unpublished observations). This is the commonest neurological manifestation of vitamin B12 deficiency (see for example Shorvon et al., 1980) and its presence might have been anticipated in some cases on statistical grounds. (4) Demyelination is a prominent feature of the neuropathology of vitamin B12 deficiency in the spinal cord (SCD) and brain; and, as already noted, of inborn errors of vitamin B12 metabolism (Surtees et al., 1991). (5) Recently, a myelopathy which neuropathologically resembles SCD has been described in AIDS patients in the absence of vitamin B12 deficiency (Petito et al., 1985). It is unclear whether the mechanism is viral or metabolic. At the very least, it may be asked whether the associated vitamin B12 deficiency from any cause is aggravating the underlying MS or hindering the process of remyelination? Although some of the patients studied have seemed to do well on vitamin B12 therapy (Reynolds, unpublished data), such uncontrolled observations are notoriously unreliable in MS. Furthermore, for many years vitamin B12 injections have been used occasionally for placebo purposes in the treatment of MS. Although some patients were impressed with their apparent neurological benefit, there was no controlled support for this conviction (Simpson et al., 1967). Clearly, controlled treatment studies will
be required in patients with MS who have been separated into those with or without a disturbance of vitamin B12 metabolism. Finally, it is to be hoped that these predominantly clinical observations will stimulate further basic research on the role of vitamin BI2 and methylation in myelin formation and integrity and in demyelinating disorders. Little is known about the requirements of the central nervous system for vitamin B12, nor the forms in which it is needed or mechanisms by which it is transported across the blood-brain barrier. Such research would assist in the evaluation of the most appropriate form, dose or duration of therapy for optimum treatment of vitamin B12-related neurological disorders (Reynolds, 1976: Lazar and Carmel, 1981).
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