The most important aspects are the history and the physical examination. In the case of a woman, if virilization is evident, laboratory analysis of dehydroepiandrosterone (DHEA)-sulfate and testosterone may need to be obtained. Some authors have suggested that total testosterone level alone may be adequate to screen for a virilizing tumor. If a thyroid disorder is suspected, obtaining a thyrotropin level is indicated.
If telogen effluvium is present, laboratory analysis of serum iron levels or a biopsy to note an underlying papulosquamous disorder may be indicated. Telogen effluvium may accelerate the course of pattern alopecia. Iron deficiency is a common and reversible cause of telogen effluvium. A normal CBC count does not exclude iron deficiency as a cause of hair loss. While a low ferritin level is always a sign of iron deficiency, ferritin behaves as an acute phase reactant, and levels may be normal despite iron deficiency. Iron, total iron-binding capacity, and transferrin saturation are inexpensive and sensitive tests for iron deficiency.
Diffuse alopecia areata may mimic pattern alopecia. The presence of exclamation point hairs, pitted nails, or a history of periodic regrowth or tapered fractures noted on hair counts suggests the diagnosis of diffuse alopecia areata.
Köse and Güleç examined the value of dermoscopy in the study of alopecias, finding that hair diameter diversity was seen in every patient with androgenetic alopecia. This was an essential but not specific finding of this alopecia because it was also present in alopecia areata, chronic telogen effluvium, and primary cicatricial alopecia. However, peripilar signs and empty follicles were indicative of androgenetic alopecia, as they were confined to this patient group. 
A biopsy is rarely necessary to make the diagnosis of androgenetic alopecia. If a single biopsy specimen is obtained, it should generally be sectioned transversely if pattern alopecia is suspected. Some dermatopathologists recommend that if a biopsy is to be performed, a sample should be obtained from 2 sites: one for horizontal sectioning and one for vertical sectioning of the hair follicles. Other dermatopathologists point out that one may commonly obtain sufficient information from serial vertical sections to diagnose the condition.
In pattern alopecia, hairs are miniaturized. In evolving-pattern alopecia, the diameter of hair shafts varies. Fibrous tract remnants (so-called streamers) can be found below miniaturized follicles. Although androgenetic alopecia is considered a noninflammatory form of hair loss, at times, a superficial, perifollicular, inflammatory infiltrate is noted. A mildly increased telogen-to-anagen ratio is often observed.
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