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Disorders of skin appendages


Noninflammatory alopecia

Transverse (horizontal) sections are generally best for evaluation of noninflammatory alopecia. Vertical sections may be used if serial ribbons of sections are cut from the block. A combination of vertical and transverse sections is always acceptable.

Pattern alopecia (androgenetic balding)

Key Features

  • Miniaturization of follicular units

  • Variability in diameter of follicles (anisotrichosis)

  • In vertical sections, hairs extend to variable depths in proportion to their diameter

  • Decreased anagen/telogen ratio

  • Many fibrous tract remnants with normal diameter and vascularity

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.

Fig. 15.1, (A and B) Pattern alopecia. (C) Solar elastosis and narrow fibrous tract remnants in pattern alopecia (Verhoeff–van Gieson stain). (D) Normal elastic tissue pattern for comparison (Verhoeff–van Gieson stain)

Telogen effluvium

Key Features

  • Many telogen hairs

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.

Fig. 15.2, Telogen effluvium: telogen hair

Trichotillomania (trichotillosis)

Key Features

  • Empty anagen follicles

  • Many catagen hairs characterized by apoptotic keratinocytes ( Fig. 15.3C )

  • Melanin casts within the follicular canal

  • Trichomalacia

Fig. 15.3, Trichotillomania

Traction alopecia

Key Features

  • Resembles trichotillomania histologically

Inflammatory nonscarring alopecia

Either vertical or transverse (horizontal) sections may be used, but serial ribbons of sections should always be cut from the block. A combination of vertical and transverse sections is always acceptable.

Alopecia areata

Key Features

  • Lymphoid inflammation at the level of the hair bulb

  • Lymphocytes within fibrous tract remnants

  • Eosinophils within fibrous tract remnants

  • Melanin within fibrous tract remnants

  • Follicular miniaturization

  • Decreased anagen/telogen ratio

  • Increase in catagen hairs

  • Melanin casts within the follicular channel

  • Dilation of follicular infundibula

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.

Fig. 15.4, Alopecia areata

Differential Diagnosis

Pattern alopecia

  • Shares follicular miniaturization, decreased anagen/telogen ratio, and many fibrous tract remnants

  • Lacks catagen hairs, melanin casts in follicular channels, lymphoid inflammation at the level of the hair bulb, lymphocytes within fibrous tract remnants, eosinophils within fibrous tract remnants, and melanin within fibrous tract remnants

Trichotillomania

  • Shares catagen hairs and melanin casts in follicular channels

  • Lacks follicular miniaturization, lymphoid inflammation at the level of the hair bulb, lymphocytes within fibrous tract remnants, eosinophils within fibrous tract remnants, and melanin within fibrous tract remnants

Table 15.1
Comparison between alopecia areata, pattern alopecia, and trichotillomania
Characteristic Alopecia areata Pattern alopecia Trichotillomania
Miniaturization Yes Yes No
Anagen/telogen ratio Decreased Decreased Variable
Fibrous tract remnants Increased Increased Normal
Catagen hairs Common Rare Common
Pigment in hair canal Common No Common
Pigment in fibrous tract Common No No
Lymphs around bulb Common No No
Lymphs in fibrous tracts Common No No
Eosinophils in fibrous tracts Common No No

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