Bilateral Reversed Palmaris Longus Muscle and the Connection to Down syndrome: A Case Report

Bilateral Reversed Palmaris Longus Down syndrome

Abstract

Objective: The palmaris longus muscle is located in the forearm's anterior or flexor compartment and exhibits a wide range of anatomical variations. Reversed palmaris longus muscle, with the muscle belly at the distal attachment, is rare, and the bilateral reversed variant is even more uncommon. Here, we present a case of bilateral reversed palmaris longus muscle in a donor with Down syndrome and explore its genetic, morphological, clinical, and surgical implications.

Methods: This case details the discovery of a bilateral reversed palmaris longus muscle in a donor with a history of Down syndrome. Images of the variation were obtained and measurements were recorded.

Results: A reversed palmaris longus muscle was observed in the anterior or flexor compartment of both forearms. On the right forearm, a proximal tendon was followed by a distal muscle belly in the wrist, with two distal tendon attachments. The left reversed palmaris longus muscle had a proximal tendon followed by a distal muscle belly and a single distal tendon attachment. No other anatomical abnormalities were observed in the anterior forearm bilaterally.

Conclusion: This case, to the knowledge of the authors, details the first documented instance of bilateral reversed palmaris longus muscle in an individual with Down syndrome. Although the relationship between Down syndrome and palmaris longus muscle variants has rarely been explored, abnormal gene expression may contribute to this association. This case aims to increase awareness and offer insight into an underrecognized variant of the palmaris longus muscle, highlighting the importance of identifying such variants in clinical evaluation and surgical planning.