Objectives To determine the correlation of the muscle pathological findings with the clinical variables in inflammatory myositis (IM) patients

Methods 91 IM patients stratified by the Bohan and Peter criteria who were attended at the Rheumatology clinic, Chiang Mai University Hospital from January 2003 to December 2010 were retrospectively identified. All had the availability of the fresh frozen sample muscle biopsies in which five micron cryostat sections were prepared and stained with H and E. All the muscle biopsies were evaluation by an experienced muscle pathologist. Four domains of the muscle pathological findings consisted of inflammation (IF), vasculitis (V), muscle (M), and connective tissue fibrosis (C) were scored. Scoring of each domain was performed by using a Likert scale as the followings; IF (0=inflammatory cell <4 cell at 20X; 1=1 cluster (≥10 cells); 2 = 2 clusters; 3 = ≥3 clusters), V (0 = none; 1 = vasculitis of 1 vessel; 2 = 2 vessels; 3 = ≥3 vessels) and C (0 = none; 1 = thin with angular fibers; 2 = moderate thick with blunt fibers; 3 = thick with round fibers). Muscle domains included muscle atrophy (0 = ≤5% of total area; 1 = 6-25%; 2 = 26-50%; 3 ≥50%); degeneration (0 = ≤5% of total area; 1 = 6-25%; 2 = 26-50%; 3 ≥50%); internal nuclei (0 = ≤3/100 fibers; 1 ≥3/100 fibers); invasion of non-necrotic fibers (0 = none; 1 = 1 fascicle; 2 = 2 fascicles; 3 ≥3 fascicles). The demographic data, muscle strength (0-5) and muscle enzymes were recorded. Spearman’s rank correlation coefficients were performed to determine the correlations between the pathology scores and the other variables.

Results Mean (SD) age was 46.5 (13.2) years. Mean duration from weakness to biopsy performed was 65.9 (109.2) days. 70 (76.9%) were female. There were four subgroups of IM patients including 54.9% IM associated with connective tissue disease, 29.7% idiopathic polymyositis, 11.0% idiopathic dermatomyositis, and 4.4% IM associated with malignancy. Mean (SD) values were: proximal muscle strength of upper limb (MUL) 3.5 (0.8), lower limb (MLL) 3.3 (0.8); creatinine kinase (CK) 3912.3 (4538.6), AST 268.8 (500.9), ALT 139.6 (181.8); IF 1.2 (1.7); V 0.2 (1.1); M: atrophy 1.6 (1.0), degeneration 0.6 (0.8), internal nuclei 0.3 (0.5), invasion of non-necrotic fiber 0.1 (0.5); C 0.6 (0.7).

Correlation coefficients of the muscle pathology scores with the other variables of 91 IM patients were:

Conclusions Muscle strength showed significantly low inverse correlation with the degeneration and connective tissue fibrosis scores. There were significantly low correlation of CK and ALT with the degeneration, invasion of non-necrotic fiber, and connective tissue fibrosis scores. No significant correlation of the muscle strength and enzymes with the inflammation were observed. The connective tissue fibrosis and degeneration scores may be a useful outcome measure of muscle damage in IM patients.

Disclosure of Interest None Declared