Patients with asymmetric sensory and motor deficits should be considered distinct from MMN because of important differences with respect to clinical and laboratory features. These patients have multifocal acquired demyelinating sensory and motor (MADSAM) neuropathy.
Like patients with MMN, those with MADSAM neuropathy experience a subtle onset and slow progression. Like MMN, upper extremities are usually involved first. Cranial neuropathies may occur, such as optic neuritis as well as palsies of the third, fifth, and seventh nerves. Deep tendon reflexes are usually abnormal in a multifocal distribution. However, as the disease progresses, there may be complete areflexia. Unlike MMN, but similar to CIDP, CSF protein is elevated in the majority of patients with MADSAM neuropathy. MADSAM neuropathy is not associated with anti-GM1 antibodies. Motor nerve conduction studies show findings similar to those seen in MMN or CIDP. However, in contrast to MMN, sensory nerve conduction studies are also abnormal. The clinical and laboratory features of MADSAM neuropathy may strongly resemble those of hereditary neuropathy with liability to pressure palsy (HNPP). Genetic testing for HNPP may be necessary in some patients being evaluated for MADSAM neuropathy, especially if distal motor latencies are prolonged.
In retrospective series, patients with MADSAM neuropathy show responses to IVIg similar to those seen in CIDP. Also similar to CIDP (but distinct from MMN), patients with MADSAM neuropathy respond to treatment with corticosteroids.
This is the main reason, the authors believe, to differentiate MADSAM neuropathy from MMN. Corticosteroids are a treatment option for patients with MADSAM neuropathy but should be avoided in patients with MMN.