Differential Diagnosis for FSH <1 in a 34-year-old Female
Single Most Likely Diagnosis
- Hypothalamic amenorrhea: This condition is characterized by low FSH levels due to decreased gonadotropin-releasing hormone (GnRH) secretion, often caused by stress, excessive exercise, or significant weight loss. It is a common cause of low FSH in young women.
Other Likely Diagnoses
- Pituitary tumor or hypopituitarism: A non-functioning pituitary tumor or other forms of hypopituitarism can lead to decreased FSH secretion. This would be suspected in the presence of other pituitary hormone deficiencies or symptoms suggestive of a pituitary mass.
- Hyperprolactinemia: Elevated prolactin levels can suppress GnRH secretion, leading to low FSH levels. This could be due to a prolactinoma or other causes of hyperprolactinemia.
- Polycystic ovary syndrome (PCOS) with low FSH: While PCOS is typically associated with high LH and normal or high FSH, some cases can present with low FSH, particularly if there is significant androgen excess or insulin resistance.
Do Not Miss Diagnoses
- Pituitary apoplexy: A sudden loss of pituitary function due to hemorrhage or infarction of a pituitary tumor can present with acute symptoms and low FSH levels. This is a medical emergency requiring prompt diagnosis and treatment.
- Cranial radiation exposure: Previous radiation therapy to the brain can lead to hypopituitarism, including low FSH levels, years after the initial treatment.
- Genetic disorders affecting the pituitary gland: Certain genetic conditions, such as Kallmann syndrome, can affect GnRH secretion and lead to low FSH levels.
Rare Diagnoses
- Gonadal dysgenesis: Rare genetic disorders affecting gonadal development, such as Turner syndrome or Swyer syndrome, can present with low FSH levels, although these are typically diagnosed earlier in life.
- Autoimmune hypopituitarism: A rare condition characterized by autoimmune destruction of the pituitary gland, leading to hypopituitarism and low FSH levels.
- Lymphocytic hypophysitis: An autoimmune inflammation of the pituitary gland that can cause hypopituitarism, including low FSH levels.