Differential Diagnosis for Amenorrhea

The patient presents with secondary amenorrhea, having not had a period in 6 months, with a history of recent intense physical activity and the use of stimulant medication. The following differential diagnoses are considered:

• 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 and, subsequently, the ovaries. The patient's history of intense running and training for a half marathon, followed by cessation, and the use of Vyvanse (a stimulant), could disrupt the hypothalamic-pituitary-gonadal axis, leading to amenorrhea. The fact that she had two cycles after starting the stimulant medication but then stopped suggests an initial disruption that may have been exacerbated by other factors such as stress or residual effects of intense exercise.

• Other Likely Diagnoses

  • Polycystic Ovary Syndrome (PCOS): Although the patient's hormonal labs were mostly normal, PCOS can present with irregular periods and is a common cause of secondary amenorrhea. The low estrogen level could be seen in PCOS, especially if the patient was not in the follicular phase during testing.
  • Thyroid Dysfunction: Abnormal thyroid function can cause menstrual irregularities. Although not mentioned, thyroid function tests (TFTs) are crucial in the evaluation of amenorrhea, and even mild thyroid dysfunction can affect menstrual cycles.
  • Pituitary Adenoma: A non-functioning pituitary adenoma could compress the pituitary stalk, leading to hypogonadotropic hypogonadism and amenorrhea. The normal hormonal labs make this less likely, but it cannot be ruled out without imaging.

• Do Not Miss Diagnoses

  • Pregnancy: Although the patient is taking prenatal vitamins, suggesting she is either pregnant or planning to become pregnant, a pregnancy test is essential to rule out pregnancy as a cause of amenorrhea.
  • Hyperprolactinemia: Elevated prolactin levels can suppress the hypothalamic-pituitary-gonadal axis, leading to amenorrhea. This could be due to a prolactinoma or other causes of hyperprolactinemia.
  • Premature Ovarian Failure (POF): Now more commonly referred to as Premature Ovarian Insufficiency (POI), this condition involves the loss of function of the ovaries before age 40. It is a less common cause of secondary amenorrhea but is critical to diagnose due to its implications for fertility and long-term health.

• Rare Diagnoses

  • Asherman Syndrome: This condition involves the formation of adhesions or scar tissue in the uterus, which can lead to amenorrhea. It is typically associated with a history of uterine surgery, infection, or other uterine trauma.
  • Genetic Disorders: Certain genetic conditions, such as Turner syndrome or androgen insensitivity syndrome, can cause amenorrhea. These are less likely given the patient's age and presentation but could be considered if other diagnoses are ruled out and there are suggestive clinical features or family history.