Multifocal motor neuropathy atypical presentation: case report

Abstract

Case report: Woman, 34 years old, with paresis that started four years ago during pregnancy, predominantly distal in the lower limbs and progression to the upper limbs. No involvement of cranial nerves and sensitivity. Initially considered a diagnosis of Myasthenia Gravis and clinical gain was observed with the use of pyridostigmine. After a few months, the patient’s symptoms recurred with asymmetric flaccid tetraparesis, predominantly in the lower limbs, associated with global areflexia and oral immunosuppressive therapy was initiated, with improvement. Electroneuromyography with normal sensory nerve conduction studies, but reductions in amplitudes in proximal compound muscle action potentials, with markedly reduced persistence in F-wave studies of the four limbs. Diffuse neurogenic changes were observed on exertion and activities such as positive sharp waves, fibrillation, fasciculations and myokymia at rest. Repetitive nerve stimulation at 3Hz without changes. A hypothesis of multifocal motor neuropathy (MMN) was then made. Treatment with intravenous immunoglobulin was performed, with significant recovery of symptoms. Discussion: MMN is a rare disease (prevalence of 0.6 per 100,000 individuals), with a predominance in men and a mean age of onset around 40 years. The differential diagnosis includes motor neuron disease and other demyelinating neuropathies. It is immune-mediated by antianglioside antibodies (anti-GM1), but they are not identified in all patients and may be present in other neuropathies. It is defined by muscle weakness predominantly distal, asymmetrical, predominantly in the upper limbs, slowly progressive, associated with reduced deep reflexes in the affected regions. The main electrophysiological characteristic is the presence of motor nerve conduction blocks (CB) outside the usual sites of compression. Conclusion: The finding that CB presents in patients with MMN suggests that nerve conduction should be extensively studied in every patient with a lowermotor-neuron syndrome to identify patients who might respond favorably to immunomodulating treatment.