Androgenetic Alopecia

Androgenetic alopecia (AGA) is the most common form of hair loss, characterised by progressive miniaturisation of genetically susceptible follicles under the influence of dihydrotestosterone (DHT).

• Affects up to 50% of men by age 50 and about 40% of women by age 70. Polygenic inheritance with AR gene involvement.
• Mechanism: 5-alpha reductase type II converts testosterone to DHT, shortening anagen and miniaturising follicles.
• Female pattern hair loss can occur with PCOS and hyperandrogenism, but most women have normal androgen levels.

• Men: bitemporal recession and vertex thinning (Hamilton-Norwood classification), progressing to a horseshoe pattern.
• Women: diffuse thinning over the crown with preserved frontal hairline (Ludwig classification), widening of the central parting, and "Christmas tree" pattern.
• Miniaturised (vellus like) hairs with increased variability in hair diameter; no scalp symptoms or scarring.
• Psychosocial distress is common.

• Clinical, with trichoscopy showing more than 20% variation in hair shaft diameter and peripilar sign.
• Pull test negative (or mildly positive).
• In women with signs of hyperandrogenism (hirsutism, acne, irregular menses): testosterone, DHEAS, SHBG, 17-OH progesterone, prolactin, TSH, pelvic ultrasound.
• Check ferritin, TSH, vitamin D, and B12 to exclude contributors.
• Exclude telogen effluvium, alopecia areata, lichen planopilaris, and traction alopecia.

• Minoxidil:
  • Topical 5% solution or foam, 1 mL twice daily (men) or 5% foam once daily (women); 2% solution in women.
  • Oral minoxidil 0.25 to 5 mg daily (low dose, off label, effective); monitor for hypertrichosis, tachycardia, fluid retention, hypotension.
  • Initial shedding at 2 to 8 weeks; maximum effect at 12 months.
• Finasteride 1 mg daily in men (reduces serum DHT by 70%; reduces PSA by about 50%; rare sexual side effects, mood effects; contraindicated in pregnancy) and dutasteride 0.5 mg daily (off label).
• Women: spironolactone 100 to 200 mg daily, cyproterone acetate 50 to 100 mg days 5 to 15 with oestrogen, oral finasteride 2.5 to 5 mg (post-menopausal or with reliable contraception).
• Adjuncts: platelet rich plasma (3 monthly sessions then maintenance), low level laser therapy, microneedling, and hair transplantation (follicular unit extraction) for stable disease.
• Counselling on lifelong treatment requirement and expected response (stabilisation in most, regrowth in about 30 to 50%).