Alopecia classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Classification

Hair Classification

• Anagen: growth phase, lasts 2-3 years (80-90% of follicles at any given time)
• Catagen: involutional phase, lasts 2-3 weeks (1-3% of follicles)
• Telogen: resting phase, lasts 3-4 months (5-10% of follicles)
  • Hair released from shaft and shed at end of telogen new cycle begins
  • Mature root sheath of telogen hair = “club” at proximal end
• Terminal hairs: large shaft diameters, bulbs extend into subcutaneous fat
• Vellus hairs: smaller in caliber and length, less pigmented
• Indeterminate hairs: size/length between that of terminal and vellus hairs

Disease Classification

Non Scarring
Diffuse

• Androgenetic alopecia
  • Most common (30-40% of men and women)
  • Genetically determined: polygenic with variable penetrance
  • Shortening of anagen phase follicular miniaturization
  • Men: M-shaped pattern along frontal hairline (temporal loss progresses to midscalp)
  • Women: more diffuse, can be difficult to distinguish from telogen effluvium
• Telogen effluvium
  • Reversible loss of mature, terminal hairs (few hundred per day)
  • Stressful event (or medication) triggers transition of more anagen hairs into telogen phase
    • Childbirth, fever, severe infection, severe psychologic stress, major surgery, crash diet
    • Drugs: heparin, antithyroid agents, anticonvulsants, hormones
  • Diffuse hair loss peaks 3-4 months after inciting event
  • Up to 30% of hairs must be lost before cosmetically apparent
• Anagen effluvium
  • Acute loss of anagen hair = 80-90% of hair
  • Occurs 10-14 days after treatment with antimitotic agents (chemo)

Focal

• Alopecia areata: incidence 1/1000
  • Smooth, discrete, circular areas of complete hair loss occurring over a few weeks
  • Exclamation point hairs: hair root narrower than normal with less pigment
  • Can occur on any hair-bearing area; nails may also have proximal pitting
  • Usually reversible: regrowth occurs over several months; 90% regrow within 2 years
  • Relapse occurs in up to 1/3
  • Decreased chance of regrowth/increased risk relapse if:
    • Prepubertal onset
    • Widespread involvement (alopecia totalis or universalis)
    • Duration > 5 years
    • History of atopy
  • Possible autoimmune mechanism: bx shows T-cell infiltrates around hair follicles
  • Positive family history in 20%
• Syphilis
  • Moth-eaten, patchy pattern of loss (may be diffuse)
  • May be associated with skin lesions of secondary syphilis, or may occur in latent stage
  • Full hairgrowth occurs after treatment of infection
• Trauma
  • Traction alopecia: due to hairstyles that impose chronic tension on hair (braids)
  • Hair loss most prominent in areas of greatest tension (margins)
  • Fine, vellus hairs present in areas of absent terminal hairs
  • Regrowth can occur in early disease (few months-yrs), but not in late disease (years)
  • Chemical trauma: repeated use of lye-containing straightening agents or hot oils for styling
  • Trichotillomania: bizarre, asymmetric pattern of broken hairs of varying length

Scarring

• Uncommon; hair loss is permanent
• Erythematous papules, pustules, or scaling centered around follicles
• Polytrichia = multiple hair shafts exiting a single enlarged orifice
• Eventual obliteration of follicular orifices
• Tinea capitis
  • Scaling and inflammation in patchy areas of hair loss, +/- lymphadenopathy
  • Usually in children
  • KOH prep positive
• Central, centrifugal scarring alopecia (a.k.a. follicular degeneration syndrome, pseudopelade)
  • Symmetric involvement of central portion of scalp with outward expansion over months/yrs
  • May be associated with pustules (folliculitis decalvans)
  • Cause unknown-> emipiric Rx with steroids, antibiotics
• Discoid lupus
  • Inflammation with plugged follicles, scale, abnormal scalp pigmentation
  • May have discoid lesions elsewhere on body