INTRODUCTIONMultifocal motor neuropathy (MMN) is a demyelinating neuropathy characterized by predominant involvement of motor nerves. MMN can mimic ALS and other lower motor neuron diseases, but, as MMN is treatable by intravenous immune globulin (IVIg) and other immunomodulating therapies (1), its differential diagnosis is important. The diagnosis of MMN is particularly difficult when its diagnostic hallmarks, conduction block (CB) and anti-ganglioside antibody are not demonstrable. In a recent study, CB was identified in only 60% of MMN patients (2). Sonography of the peripheral nerves was recently reported to detect signs of widespread demyelination including in proximal nerve segments of MMN patients with CB (3). Thus, the aim of the present study was to assess whether sonography of the nerve roots can identify nerve hypertrophy as a suggestive evidence of demyelination in MMN patients without CB and further, to help differentiate MMN from ALS. ALS was chosen for comparison because MMN is still one of the most common masqueraders of ALS when upper motor neuron sign is not obvious.
SUBJECTS AND METHODS
SubjectsRecordings were made from nine patients with MMN (all men), 22 with ALS (15 men), and from 17 normal controls (11 men) in Tokushima University Hospital, Japan. All the patients with MMN and ALS were ambulatory. The inclusion criteria for the patients with MMN were the following : (A) progressive muscle atrophy and weakness involving only a few peripheral nerves or roots, without sensory involvement, (B) lack of upper motor neuron signs, pathological reflexes, or bulbar symptoms/signs, (C) the lack of radiological abnormality of the cervical spine in an MRI scan, (D) lack of CB according to published electrodiagnostic criteria (4), and (E) most importantly, the presence of clinical improvement of the affected limb with IVIg therapy (2 g/kg given over 5 consecutive days), defined as the improvement of the pre -versus post-therapeutic modified MRC score (1 -5 scale including 4 -and 4 + grades) equal to or greater than 2 in at least two of the affected muscles (5, 6). The mean duration of our clinical follow up of the MMN patients was 42.3 months (range : 18 -107 months) and all the patients remained ambulatory. The mean number of patients undergoing IVIg treatment was 9.9 (range : 4 -17) with reproducible post-therapeutic improvement.Inclusion criterion for the ALS group was to meet either the clinically definite, or clinically probable (with or without laboratory support) revised El Escorial ALS criteria. Of note, our ALS patients had predominantly lower motor involvement at the time of the sonographic assessment, thus its clinical distinction from MMN was not straightforward. The control group was made up of individuals with no neurological symptoms or signs. Either MRI or plain four-angle x-ray of the cervical spine was performed in the control subjects to confirm the lack of significant degenerative spine disease. All the patients and control subjects gave informed consent to participate in the study. ...