313 - From Weakness to Wellness: Navigating Adult-Onset Lipid Storage Myopathy

Case Diagnosis: Adult-onset lipid storage myopathy

Case Description: 29-year-old woman presents with a 2-week history of progressive proximal muscle weakness. Examination included 4/5 strength proximally and areflexia in lower extremities. Labs showed elevated inflammatory markers and aldolase. EMG was suggestive of myopathy with myopathic units to right arm and leg. She was empirically treated with 5 days of IVIG with clinical improvement. She re-admitted within four days with worsening proximal weakness and diffuse myalgias. Found to have rhabdomyolysis with concern for acute polymyositis; treated with high-dose IV steroids. Exam worsened; notable for 1/5 strength proximally, distal muscles 4-5/5 strength, requiring maximal assistance for standing and ambulation. Deltoid muscle biopsy revealed lipid-laden type I fibers. Quantitative plasma acylcarnitine analysis suggested fatty acid oxidation deficiency. Genetic testing pending at time of submission. She was ultimately treated with high-dose L-carnitine for the diagnosis of adult-onset lipid storage myopathy. She progressed to modified independent after a 13-day course of acute inpatient rehabilitation.

Discussions: Lipid storage myopathies (LSMs) represent a heterogenous group of metabolic disorders, including fatty-acid oxidation deficiencies, characterized by lipid accumulation in muscle fibers due to lipid dysmetabolism which clinically manifest with weakness, myalgia, and fatigue. Timely diagnosis is imperative, as some LSMs can be managed by appropriate supplementation. Furthermore, differentiating metabolic myopathy from immune-mediated neuropathy or inflammatory myopathy is essential. In this case, the patient tolerated intensive rehabilitation in an acute rehabilitation setting and exhibited favorable short-term functional gains while receiving treatment with L-carnitine and riboflavin.

Conclusions: Fatty-acid oxidation deficiencies may manifest as a rare genetic variant of myopathy in adults and should be considered on the differential diagnosis of a patient presenting with progressive weakness. Prompt nutraceutical supplementation can minimize physical debility, and as seen here, patients can greatly benefit from intensive rehabilitation.