Is IVIg therapy warranted in progressive lower motor neuron syndromes without conduction block?

To evaluate the likelihood of response to IV immunoglobulin (IVIg) by studying consecutive patients presenting with progressive, asymmetric, pure lower motor neuron (LMN) limb weakness, and to determine the clinical phenotype of those who respond.

Thirty-one consecutive patients with progressive, focal-onset LMN limb weakness, without evidence of clinical upper motor neuron signs; sensory, respiratory, or bulbar involvement; or evidence of motor nerve conduction block on electrodiagnostic studies, were prospectively included in this study. Each patient underwent treatment with IVIg (2 g/kg) for a minimum of 3 months. Electrodiagnostic studies, a neuromuscular symptom score, and expanded Medical Research Council sum score were documented before and after IVIg treatment. The final diagnosis was determined after prolonged clinical follow-up.

Only 3 of 31 patients (10%) responded to IVIg. All responders demonstrated distal upper limb-onset weakness, EMG abnormalities confined to the clinically weak muscles, and a normal creatine kinase. This set of features was also identified in 31% of nonresponders presenting with distal upper limb weakness. Sex, age at onset, number of involved limb regions, and the duration of symptoms before treatment were not significantly different between groups.

The findings of the present study do not support uniform use of IVIg in patients presenting with progressive asymmetric LMN limb weakness. It is suggested that IVIg treatment be limited to patients who demonstrate clinical and laboratory features suggestive of multifocal motor neuropathy.

This study provides Class IV evidence that IVIg will not improve muscle function in 90% of patients with progressive, asymmetric, pure LMN weakness.