99mTechnetium pyrophosphate scintigraphy in the detection of skeletal muscle disease

We aimed to assess the specificity and sensitivity of (99m)technetium pyrophosphate muscle scintigraphy in the diagnostic workup of patients with suspected myopathy. We reviewed the charts of 166 patients; 52% of the subjects had myalgias, 36% had muscle weakness, 45% had an elevated serum creatine kinase (CK), and 49% had an increased C reactive protein (CRP). Scintigraphy was positive in 34 patients (20%). The test was more sensitive in the presence of muscle weakness, elevated CK, or increased CRP. The presence of myalgias did not influence the odds. Sensitivity was 60% in patients with the final diagnosis of polymyositis, dermatomyositis, or inclusion body myositis, and 70% in noninflammatory myopathies. Eight percent had false positive scintigrams. In individuals with biopsy-proven myopathy (51 subjects), the diagnostic sensitivity was 43%, and its specificity was 60%. Low positive and high negative likelihood ratios (5.0 and 0.65, respectively) document an only limited diagnostic efficiency of (99m)Tc-PYP scintigraphy in the evaluation of inflammatory and noninflammatory myopathies and suggest that the test is not helpful in the routine diagnostic workup of muscle complaints, even after a priori selection of patients for CK plus CRP abnormalities.