Prevalence of Amyloidosis in Carpal Tunnel Surgery

Amyloidosis (A) is a disease caused by the deposit of usually misfolded protein in form of amorphous fibrillar material in different tissues, which may cause their progressive dysfunction. The prevalence of amyloidosis varies by population studied and the type of amyloid. Although the prevalence in the general population is unknown, the Mayo Clinic in U.S. estimated a 1/90666. This disease generated about 0.0084 % (1367/16232579) of total hospital visits between April 2008 and April 2009 in England.

The most frequent clinical manifestations are cardiac, renal and hepatic involvement, but vary widely depending on the type of amyloidosis , organ affected and the extent of the deposits. Infiltration of amyloid may produce signs and symptoms that could be very similar to other diseases, like the rheumatologic one. This potentially polymorphous clinic presentation may suggest under-diagnosis by low clinical suspicion.

Carpal tunnel syndrome is frequent in patients with A and may be the initial manifestation. This syndrome is generated by the progressive infiltration of amyloid fibrils in the retinaculum flexor and in synovial tissue, causing compression of the medium nerve. A frequency of up to 13% of carpal tunnel syndrome has been reported in patients with primary amyloidosis.

In 1993, Breda et al. assessed 98 tendon and synovial tissue's biopsies of patients operated for carpal tunnel syndrome. The pathology revealed amyloid deposition in 12% of them, of which 8 had no evidence of systemic disease. This amyloid deposition was interpreted as probably secondary to chronic local inflammation. In 1992, Kyle et al. evaluated the incidence of systemic amyloidosis in a retrospective cohort of 35 patients with carpal tunnel syndrome and synovial local deposition of amyloidosis without evidence of systemic amyloidosis. During follow-up only 2 developed systemic amyloidosis and 11 showed only laboratory abnormalities (9 monoclonal band and 2 monoclonal light chain in the urine). In this group the amyloid deposition was identified as transthyretin (TTR) dependent in 32 of 35 cases.

Even though there are estimations regarding the prevalence of A in general populations worldwide and in patients with carpal tunnel syndrome surgery, there is no local estimation in Argentina. Additionally, it is not known if the presentation of amyloid deposits in tendon elements of pathological the carpal tunnel correlates with subcutaneous amyloid deposit.