The diseases discussed in this chapter are, for the most part, uncommon diseases. They are listed here because the cutaneous manifestations are distinctive enough to be of diagnostic help or because the cutaneous involvement is an important contribution to the morbidity of the disease.
Patients with dermatomyositis develop a cutaneous eruption in association with an inflammatory muscle disease of the autoimmune type. The most common cutaneous change is a violaceous edema of the upper eyelids. This is sometimes accompanied by redness and swelling of the entire face. In contrast to the facial lesions of lupus erythematosus, the red patches of dermatomyositis are more generalized and are less distinctly marginated. Patients with dermatomyositis may also have red to violaceous patches and plaques over the elbows, the knees, and the dorsal surface of the knuckles. The changes on the hands are similar to those found in lupus erythematosus, but the lesions are located over the joints (dermatomyositis) rather than over the phalanges between the joints (lupus erythematosus). Violaceous patches may develop over the volar tips of the fingers and on the thenar and hypothenar eminences. Telangiectasia of the posterior nail folds is regularly present. These are similar to the changes found on the hands in other collagen-vascular diseases. The severity of the cutaneous involvement does not correlate particularly well with the severity of the associated myositis. A clinical diagnosis of dermatomyositis can be confirmed by the presence of elevated muscle enzymes in the serum and by recognition of the typical inflammatory changes on muscle biopsy. Systemic malignancies of various types are found with unexpected frequency in patients with dermatomyositis who are over age 40.
Scleroderma is not ordinarily a difficult disease to recognize. It is characterized by sclerodactyly, which is defined as thickening and tightening of the skin over the fingers and hands. Other typical changes on the hand include the presence of pitted scarring on the fingertips, tapering of the fingers with loss of soft tissue from the fingertips, telangiectasia of the posterior nail fold, and curvature of the nail over the fingertip. Palmar violaceous color changes similar to dermatomyositis and lupus erythematosus may also be present. Hyperpigmentation, often interspersed with vitiligo-like hypopigmented patches, sometimes develops on the anterior chest and dorsal surface of the hands and arms. In a few patients, telangiectatic mats similar to those seen in patients with the Osler-Weber-Rendu syndrome are found on the face, upper chest, and arms. Calcinosis of the skin and subcutaneous tissue is a late finding in scleroderma. Skin biopsy, which demonstrates an increased thickness of the dermis and collagen entrapment of the sweat glands, is of help in confirming a clinical diagnosis.