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| Fig. 20.2 A, Tinea capitis. A large bald patch studded with small inflammatory papules surrounded by smaller, similar lesions. Close examination may reveal 'black dots' scattered within the bald area. B, A patch of alopecia areata showing several 'exclamation mark hairs.' |
Although many forms of alopecia can result in a circular bald patch, the most common causes are tinea capitis and alopecia areata.
Tinea capitis is a superficial fungal infection with a predilection for children, especially black children. The surface of the skin is scaly and sometimes inflamed, and small dark stubs of hair (“black dots”) may be scattered within the affected area. In this condition, the hair shaft is invaded and replaced by myriad circular fungal spores. In the United States,
Trichophyton tonsurans is usually the culprit. A circular, scaly, or crusted bald spot on the scalp of a black child should be considered to be tinea capitis until proven otherwise (Fig. 20-2A).
Alopecia areata also commonly affects children, but adults more often develop the condition. In alopecia areata, the affected areas may be totally hairless, but the scalp surface looks otherwise normal, without scaling and minimal, if any, erythema. A few short hairs may be present in the bald spot; these “exclamation mark” hairs tend to taper and lose pigment as they approach the scalp and may appear to float on the surface of the scalp (Fig. 20-2B).
