Sensory loss in multifocal motor neuropathy: A clinical and electrophysiological study

Abstract

Some patients fulfilling the criteria for the diagnosis of multifocal motor neuropathy with conduction block (MMN-CB) at the onset of disease may subsequently develop a sensory loss associated with electrophysiological sensory abnormalities. The latter could represent an overlap between MMN-CB and multifocal acquired demyelinating sensory and motor (MADSAM) neuropathy. The objective was to specify the features of MMN-CB with sensory loss (MMN-CB-Se). Five patients in a series of 11 consecutive patients who fulfilled the criteria of the American Association of Neuromuscular and Electrodiagnostic Medicine for MMN-CB at the first examination and were treated periodically with intravenous immunoglobulin (IVIg) developed sensory loss in the course of the disease. In these five patients we compared the clinical, laboratory, and electrophysiological features found after the development of sensory loss with those at the first examination. The mean time to appearance of objective sensory signs was 7.2 years. In three of the five patients the sensory loss was preceded by intermittent paresthesias in the same nerve territories as the motor involvement. The most frequent electrophysiological abnormality was amplitude reduction of sensory nerve action potentials. There were no bilateral or symmetrical clinical and electrophysiological sensory abnormalities. Anti-GM1 IgM antibodies were positive in four patients. MMN-CB-Se could be an overlap between MMN-CB and MADSAM. It shares the distribution of the sensory disorders encountered in MADSAM, but it is closer to MMN-CB on clinical and therapeutic levels. Study of more patients would be useful to classify this subgroup more accurately.

Do patients having a decrease in SNAP amplitude during the course of MMN present with a different condition?

“…This study confirms that a decrease in SNAP amplitude may occur during the course of the disease of some MMNCB patients [8,11]. Typically in this neuropathy, clinical and electrophysiological involvements are restricted to motor nerves, but previous anatomic-pathological studies have demonstrated mild axonal and demyelinating abnormalities in the sensory nerve biopsies of patients with MMNCB [2,3,7,13,15].…”

“…Two electrophysiological studies have recently reported a decrease in SNAP amplitude during the follow-up of 13 patients out of 21 MMNCB [11] and of 5 patients out of 11 MMNCB [8]. Difference in the clinical presentation between MMNCB patients with normal or decreased SNAP amplitude has not been reported in these studies, but parameters such as number of affected regions, ONLS incapacity scale and minimal dosage of IVIg to maintain clinical improvement were not evaluated.…”

“…However, recent studies have shown that SNAP amplitude may decrease during the follow-up of MMNCB [8,11]. It is unknown if these patients with decreased SNAP amplitude have a different clinical course and disability when compared with typical MMNCB.…”

Corneal confocal microscopy in chronic inflammatory demyelinating polyneuropathy

“…However, patients showing a reduction in Sural nerve action potential (SNAP) amplitude presented with a more severe disease and more prominent axonal loss 44. Some authors suggest that a subgroup of MMN patients may subsequently develop electrophysiological sensory abnormalities and this entity may represent an overlap between classical MMN and multifocal acquired demyelinating sensory and motor neuropathy 45. Further studies with larger patient numbers should evaluate the extent to which MMN patients are affected in CCM and whether this impairment is associated with particular clinical features.…”

Multifocal Motor Neuropathy: Update on Clinical Characteristics, Pathophysiological Concepts and Therapeutic Options

“…Making the correct differential diagnosis is of more than academic interest because some patients with Lewis-Sumner syndrome respond to steroids, which are ineffective or even harmful in MMN patients (see below) [121,122]. Whether it is really of clinical relevance to further separate pure MMN from MMN with sensory loss and MADSAM neuropathy clearly needs further evaluation [123]. Finally, acquired or hereditary entrapment neuropathies, e.g.…”