Case of the month.

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A 2-year-old presented to an outpatient pediatric dermatology clinic with what his mother described as the "wordt diaper rash in the world." He had a 1-year history of a nonhealing asymptomatic rash. The rash--six 0.5- to 1.cm erythematous papules and nodules on the penis, scrotum, and inguinal folds--would improve intermittently but never completely resolve. What's your diagnosis?

Diagnosis: Myofibroma

Infantile myofibromatosis is a rare and potentially life-threatening condition that should be considered in children who present with multiple skin nodules, Dr. Ivan D. Camacho reported at the annual pre-AAD meeting of the Society for Pediatric Dermatology.

"To our knowledge, this is the first report of a case of myofibromatosis of infancy confined to the genital area," said Dr. Camacho, a dermatology fellow at the University of Miami.

The myofibroma in this case was diagnosed following a punch biopsy, which demonstrated proliferative, plump, spindle-shaped cells forming interweaving fascicles imbedded in a fibromyxoid stroma. Smooth muscle actin and vimentin stains were positive, and desmin, cytokeratin, and S-100 stains were negative, which is consistent with the diagnosis of myofibroma, he said.

Myofibromas are rare, mesenchymal tumors that can present as a single lesion or in groups. They are firm, skin-colored to violaceous nodules that can involve the skin, subcutaneous tissues, striated muscles, bones, and viscera. Multiple lesions in a newborn or infant are known as infantile myofibromatosis. In most cases, myofibromas occur as solitary lesions that rarely involve the viscera.

Multiple lesions, however, often involve soft tissues, bone, and viscera and are associated with adverse prognosis and outcome, with mortality resulting from airway obstruction, intestinal obstruction, failure to thrive, or infection. In rare cases, the brain, orbit, and testis might be involved.

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The lesions should be differentiated from those associated with neurofibromatosis, fibrous hamartomas of infancy, sarcomas, granuloma gluteale infantum, and vascular tumors. Patients with multicentric cases should undergo systemic evaluation for involvement of the viscera because surgery, chemotherapy, and radiotherapy might be beneficial in those with visceral involvement. Patients without visceral involvement have an excellent prognosis, with the lesions typically regressing spontaneously over 1-2 years, as was the case in this child, Dr. Camacho said.

At follow-up, the patient's lesions were resolving spontaneously and his mother refused further work-up.