This woman has hirsutism, and polycystic ovary syndrome (PCOS) is the most likely cause. PCOS is the cause of hirsutism in 50% to 70% of premenopausal women with excess hair growth. Hirsutism is defined as the excessive growth of thick, pigmented hair (terminal hairs) in androgen-responsive areas (a “male pattern”) and affects about 8% of women. In androgen-dependent sites such as the jawline, the fine vellus hairs can be converted to thicker, courser terminal hairs like those on the underarms. The most to least common sites are the lower abdomen and areola, the chin and upper lip, between the breasts, and on the lower back.

The most important goal of the evaluation of a patient with hirsutism is to exclude the most serious causes, including androgen-secreting tumors (ovarian or adrenal). The patient must first be assessed for virilization, which is commonly due to an ovarian or adrenal tumor. Signs and symptoms of virilization include a deepening of the voice, severe acne, clitoromegaly, a decrease in breast size, and male-pattern balding. Other concerning features are rapid onset and progressive hirsutism over a short period of time (such as 1 year) or hirsutism that develops after 30 years of age. The diagnosis of PCOS is confirmed if two of the three following criteria are met: (1) oligo-ovulation or anovulation, (2) clinical or biochemical evidence of hyperandrogenism, and (3) polycystic ovarian morphology on an ultrasound when other endocrine disorders are excluded. In this patient, a transvaginal ultrasound will not be necessary to establish the diagnosis of PCOS.

Women in some family groups are predisposed to having more terminal hair growth in androgen-responsive areas. These women often develop the hairs slowly around the time of puberty and have normal menses. There is often a history of similar findings in other women in the family; however, this patient does not have a history of similar hair growth affecting the women in her family.

Hyperthyroidism may be associated with hypertrichosis, which is an excessive growth of hair but, as opposed to hirsutism, is not limited to androgen-responsive areas. The hairs often do not get as dark or thick as the terminal hairs that develop in hirsutism. Patients with hyperthyroidism may develop longer and more prominent hair growth all over their bodies, rather than in androgen-responsive sites. The hair growth is usually associated with other symptoms such as weight loss, anxiety, tachycardia, or hyperhidrosis.

Similarly, patients with porphyria can develop longer, thicker hairs in areas of sun exposure. Patients with porphyria are likely to have some skin blistering, fragility, or scarring in areas of sun exposure.