Diagnostic yield and cost-effectiveness of investigations in patients presenting with isolated lower motor neuron signs

Our objective was to investigate the yield and cost-effectiveness of investigations and therapeutic trials of intravenous immunoglobulin (IVIg) in patients presenting with isolated lower motor neuron (LMN) signs. We performed a retrospective chart review of cases diagnosed between January 2007 and September 2013. Investigation results and their impact on outcome, and outcome of IVIg treatment trials were abstracted. Cost was calculated in Canadian dollars (C$). Fifty-nine of 333 patients presented with isolated LMN signs. The majority of patients (61%) evolved to amyotrophic lateral sclerosis (ALS) within 36 months of presentation, while 37.3% remained with progressive muscular atrophy (PMA) with mean follow-up 29.6 months. Of the 1210 tests performed, 4.9% were abnormal. The diagnosis was changed in only one patient where a muscle biopsy revealed a distal myopathy. Fourteen patients received therapeutic trials of IVIg to rule out an IVIg-responsive inflammatory motor neuropathy with no objective clinical benefit. Total group cost was C$630,484.72 (C$10,686.18/patient). IVIg represented 58.7% of total costs. In conclusion, extensive investigations and treatment trials of IVIg have low yield in the work-up of patients with isolated LMN signs and are not cost-effective when clinical features do not suggest an alternative diagnosis to PMA.