(Kiosk 2) Value of Ultrasound in a Case of Neurogenic Atrophy of the Distal Vastus Lateralis in a Bodybuilder

Case Diagnosis: Neurogenic Atrophy of the Distal Vastus Lateralis in a Bodybuilder

Case Description or Program Description: A 33-year-old male bodybuilder presented with a four-month history of atrophy of his left distal vastus lateralis (VL) muscle. There was no known history of injury or associated pain, swelling, bruising, or overt weakness. The atrophy was noted in a very focal location, involving only the distal VL muscle. Ultrasound examination revealed normal-appearing muscle tissue within the proximal aspect of the VL, with an abrupt transition to hyperechoic, atrophic tissue in the distal third of the muscle. Electrodiagnostic testing revealed evidence of florid denervation and no discernable motor unit action potentials within the distal VL. The remainder of the study, including sampling of the more proximal VL, was normal.

Setting: Outpatient Private Practice

Assessment/Results: Upon repeat ultrasound of the femoral nerve and its associated branches, the terminal motor branch of the femoral nerve to the distal VL muscle was noted to demonstrate a tortuous course as it traveled deep to the hypertrophied rectus femoris muscle and emerged laterally, where it entered a more superficial fascial plane just proximal to the atrophic VL tissue. Representing a possible site of impingement or stretch injury, an ultrasound-guided hydrodissection of the femoral nerve branch using 15cc of a 5% dextrose solution was performed in this region on 3 separate occasions. The patient was noted to demonstrate improvement in muscle bulk and sonographic echotexture on follow-up.

Discussion (relevance): A literature search revealed one similar case of distal VL atrophy which had also occurred in a bodybuilder, though no ultrasound or specific treatment intervention had been performed.

Conclusions: This unique case demonstrates the potential value of ultrasound as a diagnostic and therapeutic aid while providing reference for future cases of selective mononeuropathy of a branch of the femoral nerve and associated atrophy of the distal VL.