Development of an Amyloidosis Risk Score for Positive Tenosynovial Biopsy at Carpal Tunnel Release

Tenosynovial biopsy at the time of carpal tunnel release affords a unique opportunity for the early diagnosis of amyloidosis. We aimed to build a risk score to stratify patients likely to have undiagnosed amyloidosis.

We conducted a prospective cohort study of 320 adult patients with carpal tunnel syndrome undergoing carpal tunnel release. Patients underwent tenosynovial biopsy at the time of surgery. The primary outcome measure was a positive biopsy for amyloid deposition as assessed by Congo red and sulfated Alcian blue staining. We generated a risk score by assigning points to each variable independently associated with a positive biopsy in a logistic regression model, with weights proportional to parameter estimates (log odds ratio).

The cohort mean age was 63 years, and 65% were female. Forty-nine out of 320 subjects (15.3%) had positive tenosynovial biopsies for amyloidosis. In the logistic regression model, independent predictors of a positive biopsy included age 70 to 79 years (odds ratio [OR] 14.6, 95% confidence interval [CI] 1.83-115.7) and age ≥ 80 years (OR 33.9, 95% CI 4.1-279.3) compared with age < 50 years, male sex (OR 2.6, 95% CI 1.3-5.3), and history of trigger digit (OR 2.4, 95% CI 1.2-4.9). We assigned weights proportional to the log odds ratios from the logistic model to generate a summary amyloidosis risk score based on age, sex, and history of trigger digit. A score of 0 corresponds to 2.5% risk and 6 to 75% risk.

The likelihood of a positive biopsy for amyloidosis is independently associated with older age, male sex, and history of trigger digit.

A routine biopsy strategy maximizes sensitivity for the early detection of amyloidosis with a 15% positive biopsy rate. We furthermore present a risk score for a selective biopsy strategies with associated sensitivities and specificities.