200 Section - Navigating Lower Extremity Weakness: When Common Causes Aren’t the Answer

A 65-year-old male with obesity, type 2 diabetes mellitus, and chronic obstructive pulmonary disease (COPD) presented with progressive proximal lower extremity weakness over one year, leading to recurrent falls and difficulty standing unassisted. Patient with multiple COPD exacerbations requiring prolonged courses of high-dose corticosteroids and initiation of a glucagon-like peptide-1 (GLP-1) receptor agonist for weight management, resulting in a 40-pound weight loss over six months. Examination revealed atrophy and weakness of the hip flexors. Laboratory values showed elevated creatine kinase and aldolase, with a negative myositis antibody panel. MRI demonstrated symmetric fatty infiltration of the thigh musculature, and electromyography showed features of axonal polyneuropathy and proximal myopathy. A left thigh muscle biopsy confirmed an inflammatory myopathy suggestive of inclusion body myositis (IBM).

Discussions:

This case illustrates the diagnostic challenges of progressive lower extremity weakness in patients with multiple comorbidities. Initial considerations included corticosteroid-induced myopathy, GLP-1 associated sarcopenia, and deconditioning from recurrent hospitalizations— common contributors to muscle weakness in older adults. However, the progression of symptoms, elevated muscle enzymes, and abnormal imaging warranted further evaluation. Muscle biopsy was suggestive of IBM, a rare inflammatory myopathy with insidious proximal and distal weakness that can mimic more common causes of weakness, leading to under-diagnosis. This case highlights the need for a broad differential and targeted testing when clinical findings remain unexplained. Early recognition of IBM supports timely management and avoids unnecessary medication changes.


Conclusions:

Progressive lower extremity weakness in medically complex patients warrants careful evaluation beyond common causes. Although medication effects, weight loss, and deconditioning were initially suspected, further testing was suggestive of IBM. Clinicians should remain alert to inflammatory myopathies even in multifactorial presentations. A holistic, multidisciplinary approach—incorporating thorough history-taking, medication review, and ongoing functional assessment—is essential to guide appropriate treatment, prevent further decline, and improve quality of life.