200 Section - Optimizing use of Neurodiagnostic Tools in the Rehabilitation Management of a Family Clinically Presenting with Spinal Bulbar and Muscular Atrophy - A Case Report

Case Diagnosis: Spinal and bulbar muscular atrophy is an X-linked disease affecting the motor neuron caused by a CAG trinucleotide repeat expansion in the Androgen Receptor gene. Due to unavailability of genetic testing and lack of awareness in its clinical presentation and findings in our country, patients are often misdiagnosed as Amyotrophic Lateral Sclerosis. In our study, we optimize the use of neuromuscular ultrasound and electromyography in distinguishing ALS from an ALS mimic disorder.

Case Description: Three siblings presenting with a slowly progressive disease at the age of 30 years old characterized as gradual onset of fasciculations on the chin, proximal weakness on all extremities, gynecomastia, split hand sign, tremors, and dysphonia. All three reported mild sensory impairments. Of the three, only one received a diagnosis of ALS but was lost to follow-up.

Discussions: Electrodiagnostic studies showed sensorimotor involvement with chronic neurogenic units and giant MUAPs. Ultrasound concluded using Heckmatt criteria revealed echogenicity compatible with motor neuron disorder than polyneuropathy. The ADM/APB CMAP amplitude ratio with cut off of < 1.7 classified the patients as ALS mimic disorder. Neuromuscular ultrasound showed the majority of fasciculations were in the tongue, which was uncommon for ALS. Although the modified fasciculation ultrasound score ( >7.5) classified one patient as ALS, nerve cross-sectional areas were more consistent with SBMA.

Conclusions: The use of EMG-NCS and NMUS as neurodiagnostic tools serve to support the working diagnosis. The ADM/APB amplitude ratio with a high specificity for ALS, and modified fasciculation score with  high sensitivity to distinguish ALS from SBMA, helps refine the differential diagnosis and exclusion of ALS. These findings have also guided the direction of the patients’ rehabilitation management. And with the help of a neurogeneticist, this will further guide us in the direction of getting the correct genetic test which is the gold standard in the diagnosis of SBMA.