Differential Diagnosis

Given the normal FSH, prolactin, and absence of elevated testosterone or androgen features, the differential diagnosis can be organized as follows:

• Single Most Likely Diagnosis

  • Hypothalamic amenorrhea: This condition is characterized by the cessation of menstrual cycles due to a problem with the hypothalamus, which regulates the pituitary gland. Normal FSH and prolactin levels, along with the absence of androgen excess, support this diagnosis, as it often results from stress, weight loss, or excessive exercise, leading to a disruption in the hypothalamic-pituitary-gonadal axis.

• Other Likely Diagnoses

  • Polycystic ovary syndrome (PCOS) without hyperandrogenism: Although PCOS is often associated with elevated androgen levels, some women may not exhibit these symptoms. Normal prolactin and FSH levels do not rule out PCOS, especially if there are other signs such as polycystic ovaries on ultrasound or irregular menstrual cycles.
  • Thyroid dysfunction: Both hyperthyroidism and hypothyroidism can cause menstrual irregularities. Normal FSH and prolactin do not exclude thyroid issues, as these hormones can be affected independently.

• Do Not Miss Diagnoses

  • Pituitary tumor (non-prolactinoma): Although prolactin is normal, other types of pituitary tumors could be present, affecting menstrual cycles by disrupting the normal secretion of gonadotropins. These are less common but critical to diagnose due to their potential impact on health.
  • Premature ovarian failure (POF): This condition involves the loss of ovarian function before the age of 40. While FSH is reported as normal, fluctuations can occur, and a single measurement does not rule out POF. This diagnosis is crucial due to its implications for fertility and long-term health.

• Rare Diagnoses

  • Resistant ovary syndrome: A rare condition where the ovaries do not respond to FSH, leading to amenorrhea. It's characterized by normal or elevated FSH levels, but given the normal FSH in this case, it's less likely.
  • Autoimmune disorders affecting the ovaries: Certain autoimmune conditions can lead to ovarian dysfunction. These are rare and would typically present with other systemic symptoms, but they remain a consideration in the differential diagnosis due to their potential for significant morbidity.