Peritendinitis of the Fourth Dorsal Compartment Due to Anomalous Extensor Indicis Proprius: A Case Report and Review of Anatomical Variations

Anomalous extensor indicis proprius (EIP) tendons are rare anatomical variations that can cause wrist pain and dysfunction due to tendon compression and inflammation. These variations, though often asymptomatic, are implicated in conditions such as fourth extensor compartment peritendinitis, requiring accurate diagnosis and tailored treatment. We report the case of a 56-year-old man with chronic right wrist pain lasting eight months, primarily aggravated by finger extension. Physical examination revealed a tender nodule on the dorsum of the wrist and pain elicited by the Spinner test, indicating involvement of the fourth dorsal compartment. Magnetic resonance imaging (MRI) showed an anomalous, thickened EIP tendon with peritendinitis. The patient opted for conservative management, including nonsteroidal anti-inflammatory drugs (NSAIDs) and activity modification, which led to complete symptom resolution within two weeks. This case highlights the clinical relevance of EIP tendon anomalies, which can mimic other wrist pathologies. The Spinner test and imaging modalities such as MRI are essential for diagnosis. While conservative treatment is often sufficient, surgical decompression may be necessary in refractory cases. Awareness of these rare anatomical variations is crucial for accurate diagnosis and effective management, ensuring better outcomes for patients with wrist pain.