The Role of Repeat Skeletal Muscle Biopsy: Indications, Yield and Outcomes.

INTRODUCTION/AIMS: Muscle biopsy performed to investigate weakness and/or pain may be nondiagnostic and prompt repeat biopsy. We determined the indications and yield of rebiopsy.

METHODS

Patients who underwent > 1 muscle biopsy (South Australia, 2000-2023) were identified. Biopsy indication and histological diagnosis at initial (B1) and subsequent (B2) biopsy were documented. Two histological outcomes were defined: change from non-specific (B1) to specific diagnosis (B2) (Outcome 1) or change in specific diagnosis (Outcome 2). Clinical records were reviewed to determine if rebiopsy affected clinical decision making.

RESULTS

Repeat biopsies accounted for 112/3089 (3.6%) of biopsies. The main indications for repeating a biopsy were specific diagnostic query (36/112, 32.1%), most commonly inclusion body myositis (IBM) or genetic myopathy, and unexpected clinical trajectory (74/112, 66.1%). Almost half of rebiopsies (48/112, 42.9%) met Outcome 1 (31/48) or 2 (17/48). Altered histological diagnosis impacted clinical decision-making in 17/22 (77.3%) patients. 21/34 (61.8%) with an initial non-specific myopathy achieved Outcome 1. B2 showed prominent atrophy in seven patients; 3/7 had non-specific myopathy on B1. Open biopsy method for repeat biopsy was associated with Outcome 1 or 2 (OR 4.3 [IQR 1.6-11.5], p = 0.004).

DISCUSSION: Repeat muscle biopsy achieved a specific diagnosis in 43% of cases and frequently impacted clinical decision-making. The highest yield was when IBM was suspected clinically, or when B1 showed non-specific myopathy. Non-specific myopathy may progress to histological atrophy; the role of untreated inflammation in driving this is unclear.