Pattern alopecia (androgenetic balding)

The essential histologic finding in pattern alopecia is progressive miniaturization of the follicular unit. This occurs predominantly in the central scalp, and in an asynchronous fashion. The biopsy will demonstrate variability in hair diameter. Focal spongiotic infundibulofolliculitis is common (mild seborrheic folliculitis). In long-standing cases, solar elastosis as well as elastotic degeneration of the fibrous tract remnants may be seen. Advanced pattern alopecia demonstrates a marked increase in vellus hairs (hair shaft diameter < inner root sheath diameter). Large sebaceous glands may be present, especially in males.

Telogen effluvium

Telogen effluvium has many telogen hairs. Telogen effluvium caused by premature interruption of anagen growth (such as by a febrile illness or crash diet) lacks the miniaturization of pattern alopecia. The shortened anagen cycle of pattern alopecia results in an altered anagen/telogen ratio, but not to the extent seen after febrile illness or crash dieting.

Trichotillomania (trichotillosis)

Traction alopecia

Alopecia areata

The lymphocytes appear to target melanocytes within the hair bulb. White hairs are spared. The inflammation results in damage to the hair matrix, tapered hair shafts with fracture, and miniaturization of the follicular unit.

Syphilitic alopecia

Alopecia mucinosa

Folliculotropic mycosis fungoides (cutaneous T-cell lymphoma)

Papillary dermal fibrosis is often prominent. Immunostaining may demonstrate deletion of pan-T markers such as CD7, and gene rearrangements can often be demonstrated.

Tinea capitis and Majocchi’s fungal folliculitis

Acne vulgaris

Lupus erythematosus

The features of discoid lupus erythematosus appear in a time-dependent fashion. Biopsies of early patches will show only perifollicular mucinous fibrosis and focal interface change. DIF will usually be negative at this stage. The biopsy should always be taken from an active lesion, of at least 3 months’ duration. Burnt-out patches demonstrate scarring throughout the dermis in elastic tissue-stained sections.

Lichen planopilaris (LPP)

As with lupus erythematosus, the features of lichen planopilaris appear in a time-dependent fashion. Biopsies of early patches will show only perifollicular mucinous fibrosis and focal lymphoid inflammation. These changes are most notable about the infundibulum, whereas lupus erythematosus affects the isthmus preferentially. DIF will usually be negative in the early stages, but will often show shaggy linear fibrin and cytoid bodies in more advanced lesions. Burnt-out patches demonstrate wedge-shaped scars at the level of the infundibulum.

Idiopathic pseudopelade

Most patients with ivory white scarring and spared terminal hairs have lichen planopilaris. About 10% of patients with the same clinical features have a unique histology distinct from other forms of alopecia. The dermis is shrunken and deeply eosinophilic with loss of the spaces between collagen bundles. This appearance has been likened to a sweater shrunken in the dryer. Fibrous tract remnants are broad and hyalinized, but the surrounding elastic sheath is intact. Hair granulomas may be noted in fibrous tract remnants. Elastic fibers in the surrounding dermis are thick and “recoiled” because of the contraction of the dermis.

Central centrifugal cicatricial alopecia (CCCA)

Dissecting cellulitis

Folliculitis decalvans

Patients with folliculitis decalvans present with recurrent crops of epilating follicular pustules. The histologic changes resemble those of a staphylococcal folliculitis. Staphylococci are sometimes cultured, and patients respond to prolonged courses of anti-staphylococcal therapy.

Patients with Acne keloidalis and progressive alopecia usually demonstrate overlap with folliculitis decalvans.

Böer, A, Hoene, K. Transverse sections for diagnosis of alopecia? Am J Dermatopathol. 2005; 27(4):348–352.

Childs, JM, Sperling, LC. Histopathology of scarring and nonscarring hair loss. Dermatol Clin. 2013; 31(1):43–56.

Elston, DM. What’s new in the histologic evaluation of alopecia and hair-related disorders? Dermatol Clin. 2012; 30(4):685–694.

Elston, DM. Vertical vs. transverse sections: both are valuable in the evaluation of alopecia. Am J Dermatopathol. 2005; 27(4):353–356.

Elston, DM, Ferringer, T, Dalton, S, et al. A comparison of vertical versus transverse sections in the evaluation of alopecia biopsy specimens. J Am Acad Dermatol. 2005; 53(2):267–272.

Elston, DM, McCollough, ML, Warschaw, KE, et al. Elastic tissue in scars and alopecia. J Cutan Pathol. 2000; 27(3):147–152.

Elston, DM, McCollough, ML, Bergfeld, WF, et al. Eosinophils in fibrous tracts and near hair bulbs: a helpful diagnostic feature of alopecia areata. J Am Acad Dermatol. 1997; 37(1):101–106.

Jackson, AJ, Price, VH. How to diagnose hair loss. Dermatol Clin. 2013; 31(1):21–28.

Olsen, EA, Bergfeld, WF, Cotsarelis, G, et al. Summary of North American Hair Research Society (NAHRS)-sponsored Workshop on Cicatricial Alopecia, Duke University Medical Center, February 10 and 11, 2001. J Am Acad Dermatol. 2003; 48(1):103–110.

Peckham, SJ, Sloan, SB, Elston, DM. Histologic features of alopecia areata other than peribulbar lymphocytic infiltrates. J Am Acad Dermatol. 2011; 65(3):615–620.

Templeton, SF, Santa Cruz, DJ, Solomon, AR. Alopecia: histologic diagnosis by transverse sections. Semin Diagn Pathol. 1996; 13(1):2–18.

Trachsler, S, Trueb, RM. Value of direct immunofluorescence for differential diagnosis of cicatricial alopecia. Dermatology. 2005; 211(2):98–102.

Whiting, DA. Histopathologic features of alopecia areata: a new look. Arch Dermatol. 2003; 139(12):1555–1559.