Evaluation of hair loss

Abstract

Most physicians and many dermatologists find the evaluation of hair loss to be a difficult and confusing subject. The history is particularly important and should cover the questions of shedding versus thinning, duration, family history, and grooming practices. The most important feature of the physical examination is the pattern of hair loss, which can be diffuse (affecting the entire scalp) or patterned (confined to one or several portions of the scalp). Evidence of hair-shaft fragility should also be assessed. Examination of the scalp surface is best performed with magnification, and evidence of scarring alopecia (e.g., loss of follicular ostia) should be sought. Special investigative techniques include the gentle hair pull, the forcible hair pluck (trichogram), timed shed-hair counts, the hair-growth window, and scalp biopsy. The normal 4 mm scalp biopsy specimen should contain ∼40 follicles, and ∼30 of these should be terminal anagen hairs. Telogen counts >25% and a preponderance of vellus and indeterminate hairs are clearly abnormal. There is no “standard” battery of laboratory tests that must be ordered when evaluating hair loss. Choice of tests is largely guided by the history and physical findings. There are numerous ways to classify alopecia, but none is ideal. Mechanisms resulting in alopecia include congenitally insufficient number of follicles; telogen effluvium; hair-follicle destruction (scarring alopecia); hair miniaturization; hair-shaft defects; and anagen effluvium. Androgenetic alopecia is characterized by a family history of balding and typical male-patterned or female-patterned hair loss. Compared with that from a “normal” occipital scalp, a biopsy specimen from an affected area will show evidence of follicular miniaturization and an elevated telogen count. In contrast, patients with senescent alopecia have no family history of balding, and the size of follicles and percentage of telogen hairs are normal in all parts of the scalp. Alopecia areata is a nonscarring form of alopecia that can be seen clinically with a variety of patterns. In early lesions, terminal anagen hairs show peribulbar inflammation, and there may be numerous catagen/telogen hairs. In long-standing lesions, most of the follicles miniaturize and are found in the catagen/telogen phase, and anagen hairs show dystrophic shaft formation. Telogen effluvium is a diffuse form of alopecia that typically begins 3 to 4 months after a precipitating event, such as child-birth or major surgery. Follicular numbers are normal, but all parts of the scalp show an increased percentage of telogen hairs. Patients with trichotillomania , often adolescent girls, have bizarre or irregularly shaped zones of partial hair loss. A hair-growth window will show a progressive increase in hair density. Incomplete or distorted follicular anatomy is diagnostic, but increased catagen/telogen hairs, trichomalacia, and pigment casts are additional clues to the histologic diagnosis. Traction alopecia is a related form of mechanical alopecia, often caused by traumatic methods of hair styling. Pressure-induced alopecia , yet another form of mechanical alopecia, can cause temporary or permanent hair loss at the site of prolonged intraoperative pressure. Syphilitic alopecia can be found with or without other cutaneous stigmata of syphilis. Hair loss may be diffuse and noninflammatory, resembling telogen effluvium, or patchy or diffuse and inflammatory, resembling alopecia areata. Temporal triangular alopecia is characterized by a small, permanent patch of miniaturized (vellus) hairs found in newborns or young children. Children with the loose anagen hair syndrome have a subtle and irregular thinning of the hair. Anagen hairs can be easily and painlessly extracted, revealing an absence of root sheaths. The subject of scarring alopecia is controversial. Four distinctive forms (clinically or histologically or both) of primary scarring alopecia are discussed. Lichen planopilaris is characterized by interface lichenoid dermatitis of the upper follicle and is more easily diagnosed when lesions of lichen planus are found outside of the scalp, especially in conjunction with spiny follicular papules. In contrast, chronic cutaneous lupus erythematosus shows vacuolar interface alteration and granular deposits of immunoglobulin G (IgG) at the dermal/epithelial junction. Finding lesions of discoid lupus erythematosus outside the scalp assists in diagnosis. The follicular degeneration syndrome is a distinctive form of scarring alopecia that symmetrically and centrifugally involves the crown or vertex. The condition predominantly affects black adults. Premature desquamation of the inner root sheath serves as a histologic marker of the disease, although a variety of other histologic changes are typically seen. In contrast, patients with the pseudopelade of Brocq pattern of alopecia are usually whites with asymmetric, irregularly distributed patches of hair loss. Recently some authors proposed that the condition shows characteristic histologic features.