The Journal of Laryngology and Otology January 1992, Vol. 106, pp. 56-57

Metabolic stridor: bilateral vocal cord abductor paralysis secondary to hypokalaemia? S. J. MORALEE, B.Ch., M.A., P. G. REILLY, F.R.C.S. (Nottingham)

Abstract A previously unreported association between bilateral abductor paralysis and hypokalaemia is reported in a patient presenting with stridor. Both the stridor and the bilateral abductor paralysis gradually resolved as the serum potassium was corrected. A causal link is suggested though the mechanism is unclear.

Five days after admission the serum potassium was 4.5 mMol/1, the stridor was completely resolved and indirect laryngoscopy showed normal, fully mobile cords. She was discharged from hospital and potassium supplementation was added to her regular medication.

Introduction Stridor is an auditory manifestation of disordered respiratory function due to airflow changes in the larynx, trachea or bronchi, secondary to partial obstruction (Cinnamond, 1987). Consequently, pathologies causing bilateral abductor paralysis will give rise to stridor. A case of stridor due to bilateral abductor paralysis, which may have been secondary to hypokalaemia, is reported. This has not been previously reported in the literature.

Discussion Bilateral abductor paralysis is not a common sign. The commonest causes of it are thyroidectomy and peripheral neuritis (Stell and Maran, 1978). These pathologies were not evident in this case. Moreover, the response of vocal cord movement to potassium repletion suggests a causal relationship between their paralysis and the depletion. The pathophysiology of such a relationship is unclear. It is well documented that intracellular hypokalaemia causes muscle weakness, due to its central role in the excitability of nerve and muscle. The resting potential, generation of the action potential, repolarization and end plate potentials, in both nerve and muscle, are all dependent on appropriate intracellular potassium concentrations. Hypokalaemia, for reasons that are unknown, usually causes muscle weakness of the trunk or extremities (Young et al., 1983), it has not been reported to cause vocal cord paralysis. It is , therefore, unusual that in this case the trunk and extremities were spared and the larynx paralysed. Furthermore, an abductor paralysis was seen which indicates incomplete laryngeal paralysis suggesting either, sparing of the superior laryngeal nerves and cricothyroid muscles or, increased suseceptibility of the abductor fibres to hypokalaemia as compared to the abductors, a metabolic parallel to the discredited Semon's law (Semon, 1881)?

Case report A previously well 89-year-old female presented as an emergency with a five-week history of increasing shortness of breath on exercise associated with noisy breathing. She complained of no other head and neck or respiratory symptoms and was otherwise asymptomatic, specifically she had no neurological symptoms. She denied any previous operations, specifically thyroid surgery and had never smoked. Her medication on admission was frusemide 80 mg daily, taken for two months, having been increased from her usual dose of 40 mg daily because of further ankle swelling. No potassium sparing diuretics or supplements were taken. On examination, she had inspiratory stridor at rest with signs of respiratory distress but was not fatigued or cyanotic. Flexible laryngoscopy showed the vocal cords to be fixed in the paramedian position, suggestive of a bilateral abductor paralysis. Further head and neck examination was unremarkable, specifically there was no thyroidectomy scar. General examination was unremarkable and there were no other respiratory or neurological signs. She was treated with 28 per cent inhaled oxygen and in viej^ of the clinical findings a full blood count, serum electrolytesx and urea together with a chest X-ray and ECG were performed before proceeding to tracheostomy. The chest X-ray and FBC were unremarkable but the serum potassium was 1.9mMol/l (Na 128, CrlO5 and Glucose 6.5) and the ECG showed flattened T waves indicating intracellular depletion. Following a good response to inhaled oxygen, in which she became less distressed, it was decided to correct the potassium, by intravenous and then oral supplementation, before proceeding to tracheostomy. Two days later her serum potassium was 2.7 mMol/1 and the stridor was nearly resolved. Indirect laryngoscopy showed that the vocal cords were partially mobile.

Conclusion We have described a case of stridor due to bilateral abductor paralysis which suggests hypokalaemia as a treatable cause of the paralysis though the mechanism is unclear. Acknowledgements We would like to thank Mr P. J. Bradley for allowing us to report his patient. References Cinnamond, M. J. (1987) Stridor. In Scott-Brown's Otolaryngol-

Accepted for publication: 21 August 1991. 56

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CLINICAL RECORDS

ogy 5th edition, Vol. 6. (Evans, J. N. G. and Kerr, A. G., eds.) Butterworths: London p. 420. Semon, F. (1881) Clinical remarks on the proclivity of the abductor fibres of the recurrent laryngeal nerve to become affected sooner than the adductor fibres, or even exclusively, in cases of undoubted central or peripheral injury or disease of the roots or trunks of the pneumogastric, spinal accessory or recurrent nerves. Archives of Laryngology, 2: 197. Stell, P. M. , Maran, A. G. D. (1978) Vocal cord paralysis. In Head and Neck Surgery, 2nd edition, (Stell, P. M. and Maran, A. G. D., Eds.) William Heinemann: Oxford, p. 198. Young, R., Bradley, W., Adams, R. (1983) Approach to clinical

Key words: Vocal cord paralysis

myology. In Harrison's Principles of Internal Medicine 10th edition. (Petersdorf, R., Adams, R., Braunwald, E., Isselbacher, K., Martin, J., Wilson, J. eds.), McGraw-Hill, p. 2171-2173. Address for correspondence: Dr S. J. Moralee, Department of Otolaryngology, Melbourne University, 32 Gisbourne Street, East Melbourne, Victoria 3002, Australia.

Metabolic stridor: bilateral vocal cord abductor paralysis secondary to hypokalaemia?

A previously unreported association between bilateral abductor paralysis and hypokalaemia is reported in a patient presenting with stridor. Both the s...
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