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Dermatomyositis
Dermatomyositis is an autoimmune connective tissue disease (AI-CTD) that may overlap with other AI-CTDs, in particular systemic sclerosis. It may be triggered by outside factors, most commonly malignancy (e.g. breast cancer, ovarian cancer) and occasionally drugs (e.g. ‘statins’) or rarely infectious agents (e.g. picornavirus).
• Often clinical and laboratory evidence of proximal inflammatory myopathy (the term polymyositis is used when the disease affects muscle only; Table 34.1); patients may report difficulty combing hair or rising from a sitting position.
Table 34.1
Revised classification system for the idiopathic inflammatory dermatomyopathies.
* In up to 25% of adults; ovarian, colon, breast, lung, gastric, pancreatic carcinomas (nasopharyngeal in Southeast Asian populations), and lymphoma; risk decreases to normal after 2–5 years.
** Systemic sclerosis > SLE, Sjögren’s syndrome, rheumatoid arthritis.
† Provisional = cutaneous findings without muscle weakness and with normal muscle enzymes for >6 months; confirmed = for 24 months.
• May affect the skin only (amyopathic dermatomyositis, formerly termed dermatomyositis sine myositis; see Table 34.1); Fig. 34.1 outlines an approach to the diagnosis of this form of dermatomyositis.
Fig. 34.1 Approach to adult dermatomyositis. The approach for children is similar but without the malignancy evaluation. Some authors classify patients with no evidence of myositis for 6 months after the onset of skin disease as having amyopathic dermatomyositis, but such individuals may go on to develop muscle disease. If planning administration of chronic systemic CS, a baseline DEXA bone density scan is recommended. CT, computed tomography; DLCO, diffusing capacity of the lung for carbon monoxide; PFTs, pulmonary function tests.
• Characteristic cutaneous findings include a violaceous hue of the upper eyelids with periorbital edema (Fig. 34.2) and nailfold telangiectasias (Fig. 34.3), as well as the cutaneous findings outlined in Table 34.2 and represented in Fig. 34.4A; these may precede systemic manifestations (Fig. 34.4B).
Fig. 34.2 Dermatomyositis – eyelid edema and heliotrope sign. A Inflammation of the upper eyelids can be more subtle in darkly pigmented skin; note involvement of the lateral nasal root and the cheeks. B The characteristic pink-violet color is seen with involvement of the hairline, lower forehead, upper eyelids, and cheeks; the edema is striking and involves the nasal root as well as the eyelids. B, Courtesy, Jean L. Bolognia, MD.
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