Anterior horn cell involvement in myelitis with atopic diathesis (atopic myelitis).

To clarify the involvement of anterior horn cells in myelitis with atopic diathesis (atopic myelitis), 20 patients with atopic myelitis were subjected to neurological evaluation, concentric needle electromyography (EMG), spinal cord magnetic resonance imaging (MRI) and motor and somatosensory evoked potentials. Apparent muscle atrophy was present only 1 of 20 patients (5%) and the rests clinically showed no lower motor neuron sign. On needle EMG, 12 patients (60%) showed varying degrees of lower motor neuron involvement. On-going denervation potentials, such as fasciculation potentials, fibrillation potentials and positive sharp waves, were seen in 5 patients and chronic neurogenic patterns, such as giant and polyphasic motor unit potentials with reduced recruitment patterns, in 12 patients. In 4 patients, the segments of lower motor neuron involvement on needle EMG were beyond those of the spinal cord lesions shown by MRI. In 2 patients showing on-going denervation potentials, such immunotherapies as plasma exchange and intravenous immunoglobulins, were applied and effective clinically as well as electrophysiologically. Therefore, varying degrees of subclinical anterior horn cell involvement seems to be common in atopic myelitis and reversible by immunotherapy.