Hand surgeons and amyloidosis specialists warning: transthyretin-associated amyloidosis with bifid median nerve as a cause of bilateral carpal tunnel syndrome. A case report and literature review.

INTRODUCTION: Approximately 75% of patients with carpal tunnel syndrome (CTS) are diagnosed as idiopathic. Despite this, the presence of an underlying cause such as an anatomical variant or a systemic disease must always be suspected, especially in cases of bilateral presentation without an obvious cause, recurrence or complications. The anatomical variant known as the bifid median nerve (BMN) is a very rare abnormality that can occasionally lead to CTS. On the other hands, transthyretin-associated amyloidosis (ATTR) is one of the possible causes of bilateral CTS. We report a case where these two very rare pathologies converge as the cause of bilateral CTS and a review of the literature. CASE REPORT: We report a 71-year-old male with prior history of lumbar canal stenosis, bilateral trigger finger, rupture of the supraspinatus muscle tendon and of the long portion of the right biceps brachial. He also had 8-year-old bilateral CTS that recurred after CTS surgery. He was surgically re-intervened and was diagnosed incidentally with BMN and an ultrasound of the other hands also showed BMN. Because of all the prior musculoskeletal history, a biopsy of the transverse carpal ligament was taken showing ATTR deposits that led to the diagnosis of cardiac ATTR wild type.
CONCLUSIONS: This case highlights the natural history of the multiple musculoskeletal manifestations related to ATTR and the importance of performing intraoperative biopsies in patients with CTS surgery as this can lead to early diagnosis of cardiac ATTR.