Amyotrophic Lateral Sclerosis in a Patient Treated for Neurosyphilis: A Case Report

Neurosyphilis is a recognized treatable mimic of amyotrophic lateral sclerosis (ALS); syphilis serology is commonly included in the work-up of suspected motor neuron disease. We describe the converse situation: neurosyphilis that delayed recognition of coexisting ALS.

A 46-year-old man with type 2 diabetes mellitus and degenerative spine disease presented with a six-month history of progressive limb weakness and gait disturbance. Serum syphilis serology was reactive (Venereal Disease Research Laboratory [VDRL] titer 1:32; Treponema pallidum hemagglutination assay [TPHA] titer 1:20,480), and cerebrospinal fluid (CSF) showed a mild mononuclear pleocytosis with raised protein and immunoglobulin G. Neurosyphilis was diagnosed and treated with a 14-day course of intravenous penicillin. The subsequent course was followed with neuroimaging and electrodiagnostic studies.

Despite treatment and resolution of the CSF pleocytosis, weakness and wasting progressed and bulbar involvement developed. Examination showed combined upper and lower motor neuron signs, electromyography showed an anterior horn cell pattern with widespread fasciculations, and cervical spine imaging showed degenerative changes without spinal cord compression. ALS was diagnosed at a later neurological admission.

Identifying a treatable mimic does not close the diagnostic process. Combined upper and lower motor neuron signs that continue to progress despite adequate treatment of neurosyphilis should prompt early electrodiagnostic evaluation for ALS, even though the relative contribution of each condition may remain uncertain.