Dermatomyositis with normal muscle enzymes: a single blind study of the diagnostic value of thallium-201 scanning

Background It is well documented that the classic cutaneous lesions of dermatomyositis can precede the onset of muscle involvement or may occur in the absence of any detectable muscle disease by current diagnostic criteria. Thallium scanning has been reported to be a useful test in the evaluation of muscle disease in patients with dermatomyositis. Objective Our purpose was to examine the utility of thallium scanning in patients with dermatomyositis with normal muscle enzymes. Methods In this single blind study we used thallium-201 scanning to evaluate 5 patients who presented with classical clinicopathologic dermatomyositis but with normal levels of serum muscle enzymes. A positive control patient with active myositis and a negative control patient were also examined. Results All patients had muscle groups with decreased signal intensity on thallium scanning. Even the negative control patient demonstrated marked asymmetry of several different muscle groups. These results are very different from those previously reported. Conclusions Non-invasive radiologic examinations clearly have a role in the evaluation of patients with dermatomyositis sine myositis or dermatomyositis. We have previously reported that magnetic resonance imaging and ultrasound are useful adjunctive tests. However, thallium scanning does not seem to be useful in the evaluation of patients with dermatomyositis with normal muscle enzymes. Thallium scanning appears to be a very sensitive test. However, the abnormal findings on every patient, including the negative control patient, suggest a very low specificity.