Ī thorough review of systems, past medical history, and the patient's medication list is important to ensure other causes are not present for hair loss or other reasons for the unmasking of the androgenetic alopecia.
Dermoscopy shows miniaturized hair and brown perihilar casts which can help differentiate from diffuse alopecia areata that mimics male pattern baldness as diffuse alopecia areata will have tapered fractures such as exclamation point hairs. A biopsy is usually not necessary unless the diagnosis is unclear. Shedding of 100 hairs a day (exogen) is normal.Īndrogenetic alopecia is usually diagnosed clinically with a history of gradual onset, occurring after puberty, and often but not necessarily, a family history of baldness. The normal hair growth cycle consists of four phases: anagen (growth), catagen (involution), telogen (resting), and exogen (shedding of hair). Eighty percent to 90% of hair is in the anagen phase which lasts 2 to 6 years and determines the hair length less than 5% are in catagen, and the rest are in telogen. Type 2 5 alpha-reductase enzymes are in the outer root sheath of hair follicles, epididymis, vas deferens, seminal vesicles, and prostate. Type 1 5 alpha-reductase enzymes are in sebaceous glands, keratinocytes, and sweat glands. Type 2 5 alpha-reductase enzyme plays a greater role in androgenetic alopecia. The 5 alpha-reductase converts testosterone to DHT (dihydrotestosterone), which has a much greater affinity for the androgen receptor. There are two major isoforms of the 5 alpha-reductase enzyme. Īndrogenetic alopecia patients have higher production of dihydrotestosterone, and higher levels of 5 alpha-reductase and androgen receptors in balding scalp. Pathological specimens will show a decreased 5:0 ratio of anagen to telogen hair where the norm is 12:1. In androgenetic alopecia, excessive activation leads to follicular miniaturization through a progressively shorter anagen phase, resulting in thinner and shorter hair follicles which in the end may not even penetrate through the epidermis. Activation of the androgen receptor shortens the anagen or growth phase in the normal hair growth cycle.
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