Androgenetic Alopecia

Androgenetic Alopecia - Hair's The Problem?

⭐ Androgenetic alopecia is the most common cause of hair loss, featuring progressive hair follicle miniaturization due to genetic and androgenic factors.

• AKA: Male/Female pattern baldness.
• Pathophysiology: Dihydrotestosterone (DHT) binds to androgen receptors in hair follicles → shortens anagen (growth) phase → follicular miniaturization.
  • Enzyme: 5α-reductase (converts testosterone to DHT).
• Genetics: Polygenic inheritance.
• Presentation: Gradual, patterned hair thinning; non-scarring alopecia.
  • Men: Bitemporal recession, vertex thinning (Hamilton-Norwood scale).
  • Women: Diffuse thinning over crown, frontal hairline often preserved (Ludwig scale).

Androgenetic Alopecia - DHT's Bad Hair Day

• Etiology: Polygenic inheritance; androgen-dependent.
• Pathogenesis:
  • Testosterone converted to Dihydrotestosterone (DHT) by 5-alpha reductase (Type 2 in hair follicles).
  • DHT binds androgen receptors → follicular miniaturization.
  • ↓ Anagen (growth) phase, ↑ Telogen (resting) phase.
  • Terminal hairs transform into vellus-like hairs.

⭐ Dihydrotestosterone (DHT), converted from testosterone by 5-alpha reductase (type 2 predominantly in hair follicles), is the primary androgen responsible for follicular miniaturization in AGA.

Androgenetic Alopecia - Thinning Threads

• Presentation: Gradual, progressive hair thinning; non-scarring alopecia.
• Pathognomonic: Miniaturization of terminal hairs into vellus-like hairs.
• Onset: Typically post-pubertal; earlier onset may predict ↑ severity.
• Male Pattern (Hamilton-Norwood):
  • Bitemporal recession (M-shape).
  • Vertex thinning/balding.
• Female Pattern (Ludwig/Olsen):
  • Diffuse thinning over crown/vertex.
  • Frontal hairline often preserved (Christmas tree pattern).

⭐ Male AGA typically follows Hamilton-Norwood patterns (bitemporal recession, vertex thinning), while female AGA often presents as diffuse thinning with frontal hairline preservation (Ludwig/Olsen patterns).

Androgenetic Alopecia - Scalp Detective Work

• Clinical Dx: Patterned hair loss (Hamilton-Norwood in men, Ludwig in women).
• Scalp Exam: Miniaturized hairs, ↑vellus hairs.
• Pull Test: Usually negative (<10% hairs removed with gentle pull of ~60 hairs); positive if active shedding (e.g., co-existing telogen effluvium).
• Trichoscopy (Dermoscopy):
  • Key diagnostic tool.

  • ⭐ Key trichoscopic finding in AGA is hair diameter diversity (anisotrichosis) with >20% variation, alongside vellus hairs and perifollicular pigmentation.

  • Yellow dots (sebaceous glands, empty follicles).
  • Brown perifollicular halo.
• Biopsy (rarely needed): ↑Telogen hairs, miniaturized anagen follicles; T:A ratio < 4:1 (normal >7:1).

Androgenetic Alopecia - Hair Growth Hacks

• Medical Pillars:
  • Topical Minoxidil (2%, 5%): Vasodilator, K+ channel opener.
  • Oral Finasteride (1mg/day): 5α-reductase (type II) inhibitor; ↓DHT.
    • ⚠️ Sexual dysfunction, mood changes.
  • Oral Dutasteride (0.5mg/day): Potent 5α-reductase (I & II) inhibitor; off-label.
  • Anti-androgens (Females): Spironolactone, cyproterone acetate (contraception vital).
• Procedural & Other:
  • Hair Transplantation (FUT/FUE).
  • Platelet-Rich Plasma (PRP).
  • Low-Level Laser Therapy (LLLT).
  • Microneedling.

⭐ Topical minoxidil (vasodilator, K+ channel opener) and oral finasteride (5-alpha reductase inhibitor) are first-line FDA-approved treatments for male AGA; minoxidil is first-line for female AGA, with finasteride used off-label in postmenopausal women or those not planning pregnancy.

High‑Yield Points - ⚡ Biggest Takeaways

• Androgenetic alopecia: most common hair loss; strong genetic and androgen (DHT) influence.
• Gradual onset of characteristic patterned hair loss: Hamilton-Norwood scale (men), Ludwig pattern (women).
• Pathophysiology: progressive follicular miniaturization driven by DHT.
• 5α-reductase enzyme converts testosterone to dihydrotestosterone (DHT).
• Mainstay treatments: topical Minoxidil; oral Finasteride or Dutasteride (5α-reductase inhibitors).
• A non-scarring alopecia; early intervention is key to preserve hair follicles.