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Distinguishing characteristics of alopecia secondary to child abuse include signs of trauma with underlying scalp hematoma, hemorrhage, tenderness, and irregular outlines of localized hair loss. Hair breakage and subsequent regrowth is typically at a more regular length than in chronic trichotillomania. Scaling and other signs of inflammation are absent, differentiating traumatic hair loss from tinea capitis.
In trichotillomania, look for irregular patches of alopecia with twisted or broken hairs of varying lengths. Affected areas of the scalp are not completely bald. Focal perifollicular erythema, hemorrhage, and/or crusting may also be present. These patches are commonly located on the frontoparietal or frontotemporal areas of the scalp opposite the dominant hand. Diagnosis of the habit can be confirmed by observation.
In traction alopecia, hair loss is typically at the margins of the scalp and between braids. In the area of hair loss, fine vellus hairs are typically visible. The scalp appears normal without evidence of scarring.
In pressure-induced alopecia, a well-demarcated, discrete patch of hair loss is visible. The occipital region is commonly affected.
Common mimickers of traumatic alopecia and associated findings include the following:
- In alopecia areata, there are typically smooth areas of hair loss in round, well-delineated patches. Erythema and broken hairs are absent, but “exclamation point hairs” with a thinned base are present peripherally in the patch. Alopecia may extend to involve all the hair on the body (alopecia totalis and universalis).
- Tinea capitis typically has associated scaling and erythema. Examination of plucked hairs with potassium hydroxide (KOH) and fungal culture showing hyphae are diagnostic.
- Seborrheic dermatitis is often associated with erythematous papules and plaques with waxy scale distributed on the scalp, face, neck, behind the ears, or in the diaper area.
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