Background Polymyositis (PM) is a chronic inflammatory myopathy of unclear aetiology. Clinical features of PM have been well described, but the study of the correlation between serum muscle enzymes, muscle weakness and muscle pathology is limited.
Objectives We reported the clinical correlation between serum muscle enzymes, muscle weakness and muscle pathology in Thai patients with PM.
Methods A retrospective chart review was carried out in patients with PM, age >16, who had muscle biopsy available for review, and seen during January 1986 – December 1999. The diagnosis of PM followed Bohan and Peter’s criteria. The degree of muscle weakness was graded 0–5. The degree of muscle inflammation was scored 0–4 (0%, 1–10%, 11–25%, 26–50% and >50% of inflammatory cell infiltration, respectively), and the degree of muscle destruction was scored 0–4 (0%, 1–10%, 11–25%, 26–50% and >50% of muscle fibre destruction respectively). Serum muscle enzymes including CPK, LDH and AST, which determined within 7 days prior to muscle biopsy, were used for analysis.
Results Of 163 patients, 123 had muscle biopsy performed. Only 102 specimens were available for review, of which 2 that showed granulomatous myositis were excluded due to the possibility of tuberculous myositis. Therefore, 100 charts were included for analysis. There were 22 males and 78 females, with their mean ± SD age and duration of disease of 45.0 ± 13.9 years and 6.3 ± 13.4 months, respectively. The clinical diagnoses were idiopathic PM in 37 cases, idiopathic dermatomyositis in 13, myositis associated with malignancy in 5, and PM associated with connective tissue disease in 45 (SLE in 16 cases, scleroderma in 22, MCTD in 6, and PAN in 1). The mean ± SD scores of proximal muscle weakness, muscle inflammation and destruction were 3.2 ± 0.8, 1.5 ± 1.6 and 2.2 ± 1.7, respectively. Serum muscle enzymes including CPK, LDH and AST were elevated in 87%, 92% and 82%, respectively, with a mean ± SD level of 2,352 ± 3,239 U/L, 750 ± 420 U/L and 196 ± 193 U/L, respectively. Seventy-six percent had abnormal EMG findings that were compatible with myositis. There was a good correlation between the level of serum muscle enzymes and the degree of muscle inflammation and destruction (p < 0.02). The degree of weakness correlated well with the degree of muscle inflammation and destruction (p < 0.05 and <0.01, respectively). There was no significant correlation between ESR and serum muscle enzymes, muscle weakness or muscle pathology. Patients with idiopathic PM had more severe muscle pathology than patients with PM associated with connective tissue disease.
Conclusion Serum muscle enzymes showed a good correlation with muscle pathology. The degree of muscle weakness correlated well with the degree of muscle destruction. ESR had a limited value in patients with PM.
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