A case of spontaneous acute sensory neuronopathy is described in a pre-

viously healthy 19-year-oldmale. He had marked sensory ataxia with relative sparing of cutaneous sensation. There was no recovery over 4 years. Sural nerve biopsy showed modest axonal loss. Sensory evoked potentials were mildly abnormal in the face of absent sensory nerve action potentials. The long-latency (R2) reflex was preserved whereas the short-latency (R1 ) reflex was absent. The findings indicate that loss of large-diameter (group la) ganglion cells are primarily responsible for this syndrome. Key words: MUSCLE & NERVE




Sensory neuronopathy is distinguishable from sensory neuropathy by the global, rather than distal, distribution of sensory loss, total arreflexia and absence of recordable sensory nerve action potentials in the face of normal motor action potentials.’ These features point to the dorsal root ganglion cell as the site of primary pathology. The acute form of the disease is rare, and usually, but not invariably, has been associated with systemic antibiotics, especially peni~illin.’*~*’~ We have had opportunity to study a patient with acute sensory neuronopathy, without obvious precipitating factors, and to follow him over several years. CASE REPORT

The patient, a 19-year-old man was seen initially in June 1984. Twelve days following a “flu-like” illness, he developed rapidly spreading numbness and tingling involving both arms and legs, rendering him severely ataxic. There were no complaints indicative of autonomic dysfunction. He had not been exposed to known toxins, alcohol or other

From the Department of Medicine (Division of Neurology), The University of British Columbia, Vancouver, Canada. Address correspondence to Dr. Eisen, The Neuromuscular Disease Unit (EMG), The Vancouver General Hospital, 855 West 12th Avenue, Vancouver, BC V5Z 1M9, Canada. Accepted for publication April 6, 1989. CCC 0148-639W901050381-04 $04.00 D 1990 John Wiley & Sons, Inc.

Acute Sensory Neuropathy

substance abuse and had not been treated with antibiotics or other medications. Previously he had been in good health. On examination, his mental status and cranial nerves were normal. Ocular movements were full. There was no muscle weakness. Tendon reflexes could not be elicited. He had marked truncal ataxia and dysmetria of all extremities. He was unable to walk unassisted and when attempting to do so threw his legs out aimlessly. Proprioception was lost to the level of the elbows and knees and vibration to the level of the shoulders and iliac crest. There was marked reduction of two-point discrimination in the hands and feet. In contrast cutaneous sensation was only minimally involved. Blood count, chemistry, serology, and immunology and cerebrospinal fluid analysis were normal. A sural nerve biopsy, done 5 months after onset of his disease, revealed no convincing abnormality. Nerve fascicles were surrounded by normal perineurium with normal-appearing epineural blood vessels. There were neither inflammatory infiltrates nor deposits of amyloid or other abnormal substance. Morphometric analysis of the nerve showed a myelinated fiber density of 4588/mm2 (normal range 7000- 10,000/mm2). Fiber distribution was unimodal, with more than 70% of axons being less than 3.5 microns and only about 1% larger than 8 microns. Electronmicroscopy showed rare degenerating myelinated axons. There were no examples of axonal sprouting, no evidence of


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The patient's neurological deficit 4 years after the onset of his disease had not substantially changed. Tendon reflexes were still absent. He was ambulatory with difficulty but was able to manage his own computer store. COMMENT



The clinical features of this case are typical of acute sensory neuronopathy. 1,3,13 Motor function and motor conduction velocities were normal throughout the course, a requisite for the diagnosis. The sensory deficit was global, symmetrical, and associated with total absence of tendon reflexes. Cutaneous sensation was relatively spared. This was in keeping with the modest fiber loss noted in the sural nerve, which does not contain Ia afferents. In contrast was the marked proprioceptive impairment and ataxia indicating loss of dorsal root ganglion cells, further supported by failure of any substantial recovery over 4 years.' As described above, acute sensory neuronopathy is rare.' Nosologically it may form part of a broader spectrum including acute pandysautonomia with severe sensory deficit (which involves both dorsal root ganglia and peripheral nerves)',* and possibly Guillain- Barre syndrome with sensory p r e d ~ m i n a n c e . ~ Two aspects of the electrophysiological studies deserve comment: the relatively normal median SEP (Fig. 2) and the preserved long-latency (R2) reflex in association with an absent short-latency ( R l ) component (Fig. 1). Both observations were reproducible 4 years apart. Ability to elicit an SEP in the apparent absence of a peripheral SNAP is well recognized4 and is possible because of am lification within the central nervous Under these circumstances, however, the SEP is usually small and of poor morphology, with major components either being very prolonged or absent. The near normal median SEP recordable in the presence of such se-

FIGURE 1. Long-latency ( R l ) and short-latency (R2) reflexes elicited from a normal subject (left) and the patient (right). Two traces of 200 averaged, fully rectified, responses are superimposed. The stimulus applied to the median nerve at the wrist was just sufficient to induce a small M wave. The latencies are indicated. R1 was absent in the patient.

segmental demyelination, no thinly myelinated axons and no abnormality of the unmyelinated fiber population. ELECTROPHYSIOLOGICAL STUDIES

The table summarizes the findings. He was examined twice, 4 years apart. Compound motor action potentials recorded from the thenar, hypothenar and abductor hallucis muscles were normal in latency and amplitude. F wave latencies were also normal. Motor conduction velocities of the median, ulnar and posterior tibial nerves were normal. Sensory nerve action potentials could not be elicited from the median, ulnar or sural nerves, even employing near-nerve needle recording. An H reflex was not elicited. Long-latency (R2) but not short-latency (RI) reflexes were elicited and were normal6 (Fig. 1). Median and tibial sensory evoked potentials (SEPs) could both be elicited. The median N20 was prolonged but the potential was of good morphology. Tibial P40 was either absent or, if present, very prolonged (Fig. 2). Needle EMG studies of the right deltoid, extensor digitorum communis, quadriceps, tibialis anterior and gastrocnemius were normal. 41

56.5 78 I

_J 1 PV Left Median SEP

20 ms




Left Post Tibial SEP

FIGURE 2. Median (left) and tibial (right) SEPs recorded from the patient in November 1988. Each trace is the average of two separate runs of 500 epochs each. The montages used were c4-Fz and Cz-Fz respectively.


Acute Sensory Neuropathy


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Table 1. Electrophysiological studies in sensory neuronopathy. Normal limits

Nov 1984

Nov 1988

Right median Motor latency (wrist) Motor amplitude (wrist) F wave (wrist) MCV SNAP

(4.2 rnsec >8.0 rnV 3.0 msec >12 rnV 50 rnlsec

2.4 msec 17.2 mV 27.0 msec 58.0 rnlsec Absent

2.6 rnsec 15.7 mV 25.8 rnsec 62.0 mlsec

12.5 mV 42 mlsec

3.2 msec 19.2 rnV 47.2 msec 46.0 mlsec

3.4 msec 21.6 mV 49.0 msec 45.0 rnlsec

Right posterior tibia1 Motor latency (ankle) Motor amplitude (ankle) F wave (ankle) MCV Sural SNAP


t i reflex



Thenar short-latency ( R l ) reflex

Acute sensory neuronopathy with preserved SEPs and long-latency reflexes.

A case of spontaneous acute sensory neuronopathy is described in a previously healthy 19-year-old male. He had marked sensory ataxia with relative spa...
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