Atypical carpal tunnel syndrome: A case of first lumbrical anomaly

Carpal tunnel syndrome (CTS) is the most common compressive neuropathy encountered in orthopedics and is likely caused by thickening of the transverse carpal ligament (TCL). We aim to report a rare case of atypical CTS secondary to a first lumbrical anomaly. A 20-year-old, right-handed male chef presented with numbness along the median nerve distribution of his bilateral hands, with electrophysiologic test confirming median nerve pathology and magnetic resonance imaging revealing no abnormalities of the median nerve and TCL. However, on open carpal tunnel release (OCTR), the first lumbrical muscle was observed within the carpal tunnel and radial to the median nerve despite full finger extension. There was no thickening of the transverse carpal ligament and no tenosynovitis within the carpal tunnel. OCTR effectively relieved his symptoms. An anomaly of the 1st lumbrical muscle is a possible cause of atypical CTS and may be successfully treated with OCTR with microscope magnification to improve visualization during exploration.