A Young Girl with Weather-Beaten, Waxy Knuckles

9-year-old girl of mixed Asian and Caucasian descent was referred to pediatric dermatology to evaluate skin changes affecting her knuckles. She reported a 3-month history of intermittent ‘‘burning’’ pain and swelling of her hands. This occurred after hiking, a day at the county fair, and swimming outdoors. Blistering and ulceration accompanied the most recent episode. Progressive thickening of the skin, particularly over the knuckles, was noted. The patient also complained of headaches, fatigue, and decreased appetite. Her presumed diagnosis was dermatomyositis, but the results of laboratory studies, including a complete blood count, liver function tests, creatine phosphokinase and aldolase levels, anti-nuclear antibody screen, and rheumatoid factor, were all normal. Her past medical history was remarkable for short-stature and mild rightsided weakness caused by congenital micropolygyria of the left frontal and parietal lobes. She was not taking any medications or dietary supplements. There was no family history of skin disease, unexplained anemia, or hepatic dysfunction. Physical examination revealed a well-appearing, wellnourished girl who looked her stated age. Mild erythema and subtle thickening of the skin of both dorsal hands was noted. In addition, accentuation of the skin’s normal ridges and furrows was seen, giving the hands a ‘‘weather-beaten’’ or leathery appearance. Pink, waxy plaques without scale covered the metacarpophalangeal joints, and to a lesser extent, the proximal interphalangeal joints (Figure 1). Examination of the remaining skin, hair, nails, and teeth was unremarkable. Joint swelling and hepatomegaly were not appreciated. A skin biopsy from the right dorsal hand was obtained for histopathological examination. Clinical Discussion The patient had burning and swelling of the hands and progressive skin thickening over the knuckles. The occurrence of symptoms after outdoor activities and the localization of the skin changes to exposed skin suggest that photosensitivity— an abnormal reaction to sunlight—is at play. The differential diagnosis of photodistributed skin changes in children is presented in theTable. The common feature of these disorders is an abnormal or adverse reaction of the skin to solar energy. The patient’s symptoms point to a diagnosis of erythropoietic protoporphyria (EPP). The symptoms of EPP often begin in infancy; parents note that infants may scream or cry when exposed to intense sunlight. This child’s later age at presentation points to milder manifestations. The typical skin changes occur in areas of chronic sun exposure such as the face (nose and ears) and dorsal hands; however, this child’s facial skin was normal. Acute changes after sun exposure include erythematous, edematous plaques, which may look urticarial. Chronic changes include a thickened, weather-beaten, and aged appearance to the skin, cobblestone texture, and scarring. The skin changes associated with the collagen vascular disorders lupus erythematosus and dermatomyositis may also be photodistributed. This child’s referring diagnosis was juvenile dermatomyositis (JDM), and the changes over her knuckles are reminiscent of Gottron’s papules: flat-topped, violaceous papules over the joints of the dorsal hands, seen in dermatomyositis. Other skin findings of JDM include erythema and edema of the face and eyelids (the ‘‘heliotrope rash’’), patches of purple-red erythema with fine scale on the scalp, upper trunk, and extensor surfaces, periungual telangectasia, and ragged cuticles, all of which this child lacked. The findings of atrophy, telangectasia, and dyspigmentation, termed poikiloderma, may also occur. Laboratory evaluation for JDM can reveal elevated serum creatine phosphokinase and aldolase levels, but the absence of these abnormalities does not rule out the disorder because the skin findings can be seen in isolation or precede the development of myositis. 1 Idiopathic and exogenous photodermatoses should also be considered. In these disorders, eczematous, urticarial, or bullous changes may be seen. The idiopathic photodermatoses often follow a seasonal course, flaring in spring or early summer and then improving throughout the year. A genetic basis is presumed for these disorders, but the specific genes affected have not been identified. Exogenous photodermatoses are triggered by topical or systemic agents that heighten the skin’s reaction to sunlight. Pathologic Findings