Disclosures: Roy Taborda, MD: No financial relationships or conflicts of interest

Case Description: 59 year old male presented to acute inpatient rehabilitation secondary to progressive muscular weakness. While his initial working diagnosis was myositis, his continued respiratory decline despite four weeks of high dose steroids triggered further diagnostic evaluation. Repeat electromyography (EMG) testing demonstrated early recruitment and fibrillations consistent with myositis with no peripheral nerve involvement. However, muscle biopsy of the quadriceps showed minimal inflammation and lacked sarcolemmal staining, typically seen with inflammatory myopathies. Acid maltase deficiency, a cause of metabolic myopathy, was unlikely due normal enzyme testing. The patient’s respiratory status continued to deteriorate with an acute drop in his vital capacity from 1.44 to 0.6 liters. He required urgent transfer to the intensive care unit (ICU) for continuous non-invasive mechanical ventilation. He received a 3 day course of intravenous immunoglobulin without improvements. Repeat EMG after ICU transfer revealed findings of active denervation and chronic re-innervation consistent with motor neuron disease rather than myositis. Based on clinical and electrodiagnostic findings, the patient was diagnosed with progressive muscular atrophy (PMA) also known as Duchenne–Aran muscular atrophy.

Setting:

Setting: Acute inpatient rehabilitation and hospital

Patient: 59 year old Hispanic male Assessment/

Results: Diagnosis of progressive muscle weakness in a previously healthy 59 year-old male proved challenging due to his initial inconsistent test results. Repeat EMG study eventually led to the diagnosis of PMA, an amyotrophic lateral sclerosis (ALS) variant that only affects lower motor neurons.

Discussion: The patient’s clinical presentation was atypical for the admitting diagnosis of myositis. Rapid respiratory deterioration led to repeat EMG evaluation and the eventual diagnosis of PMA.

Conclusion: Neuromuscular diseases may be challenging to diagnose. Repeat EMG evaluation may be beneficial in individuals whose diagnosis remains unclear. Early recognition of degenerative diseases can help optimize treatment and shape discussions regarding prognosis.

Level of Evidence: Level V

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PM&R Meeting Abstracts - https://pmrjabstracts.org/abstract/feeling-weak-in-the-knees-the-search-for-an-elusive-neuromuscular-diagnosis-a-case-report/