How do you differentiate among the different forms of nonscarring alopecia?

In alopecia areata, there usually are circular areas of noninflammatory, nonscarring alopecia with “exclamation point” hairs at the margins, and there may be associated nail pitting. Tinea capitis is characterized by patchy alopecia with varying degrees of erythema and scale that is KOH and/or fungal culture positive. In patient with traction alopecia, a distinct pattern that corresponds to a hair style is present (e.g., corn rows).

In trichotillomania, irregular patches of nonscarring, noninflammatory alopecia are covered with broken-off hairs of variable lengths that are scattered randomly between empty hair follicles (Fig. 66-4). Patients with trichotillomania often pull out their upper lid eyelashes but leave the lower lid eyelashes, as these are more difficult to grasp. Patients with alopecia areata may have eyelash loss on both the upper and lower lids.