Disclosures: Kathryn Slaughter, MD: No financial relationships or conflicts of interest

Case Diagnosis: A case report describing idiopathic unilateral biceps fibrosis

Case Description: A 27 year old female retired competitive swimmer with a history of multiple left shoulder dislocations more than 10 years prior presented for evaluation of small left bicep muscle. She reported left upper extremity weakness for several years, with significant side-to-side difference in arm circumference noticed after recently initiating a weight lifting regimen. Her exam was notable for decreased bicep musculature and weak supination and elbow flexion on the left. MRIs of the C-spine and shoulder were unremarkable. She was then referred for an EMG. Nerve conduction studies, including study of the lateral antebrachial cutaneous nerve, were normal. Neuromuscular ultrasound was used to confirm EMG needle placement within the atrophied biceps, which demonstrated no insertional activity and zero motor unit action potentials during activation. Needle study of all other muscles, including the brachialis, were normal. Ultrasound was also used to evaluate the biceps, which showed intact proximal and distal tendons and diffuse hyperechogenicity consistent with fibrosis.

Setting: Academic HospitalAssessment/

Results: MRI showed isolated fatty atrophic changes of the biceps brachii muscle and nonspecific proximal musculocutaneous hyperintensity without discrete lesion. Differential diagnosis included injury of the musculocutaneous nerve fascicles to the biceps, infiltrative disease of the muscle and ischemia. Muscle biopsy, muscle implant, or nerve grafting were discussed, but she deferred further treatment.

Discussion: While there are case reports of isolated muscle atrophy or fibrosis related exercise induced rhabdomyolysis, sub-clinical compartment syndrome and neuropathy, to our knowledge this is the first reported case of unilateral fibrosis of a biceps brachii muscle.

Conclusion: This case of isolated biceps atrophy highlights the usefulness of ultrasound to confirm needle placement in EMG, while also providing dynamic muscle evaluation that assists in the development of a broad differential diagnosis for uncommon presentations.

Level of Evidence: Level IV

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PM&R Meeting Abstracts - https://pmrjabstracts.org/abstract/idiopathic-unilateral-biceps-fibrosis-a-case-report/