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Risk Score for Positive Tenosynovial Biopsy for Amyloidosis at Carpal Tunnel Release
Dafang Zhang, MD
1; Philip Blazar, MD
1; Brandon E. Earp, MD
2; Kyra Benavent, BS
11Brigham and Women's Hospital, Boston, MA; 2Brigham and Women's Hospital, Harvard Medical School, Boston, MA
Introduction: Tenosynovial biopsy at the time of carpal tunnel release in select patients affords a unique opportunity for early diagnosis of amyloidosis and initiation of new disease-modifying treatment in the early stages of disease, before onset of cardiac manifestations. The primary objective of this prospective cohort study is to build a risk score, based on easily accessible risk factors independently associated with a positive tenosynovial biopsy for amyloid deposition at carpal tunnel release for patients with idiopathic carpal tunnel syndrome.
Methods: We conducted a prospective cohort study of 320 adult patients with electrodiagnostic study or ultrasound-confirmed carpal tunnel syndrome undergoing carpal tunnel release at a tertiary center. 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 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.
Results: The cohort mean age was 63 years, and 65% were female. Forty-nine 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 (OR 14.6, 95% 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 (Table 1). A score of 0 corresponds to 2.5% risk and 6 to 75% risk (Figure 1). A policy of biopsying at a risk score cutoff of ?4 optimizes trade-offs between false-positives and false-negatives, yielding 69.4% sensitivity and 79.7% specificity.
Conclusions:
The likelihood of a positive biopsy for amyloidosis is independently associated with older age, male sex, and history of trigger digit. The amyloidosis risk score is useful preoperatively when deciding whether to biopsy the tenosynovium at the time of carpal tunnel release.
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