Differential Diagnosis for a 33-year-old Woman with Irregular or Absent Periods

The patient's history and laboratory results are crucial in differentiating between potential diagnoses. The key factors to consider include the onset of symptoms after stopping the pill, coinciding with significant lifestyle changes (heavy fasting, restricted calorie intake, and high-intensity workouts), and the laboratory findings.

• Single Most Likely Diagnosis

  • Hypothalamic Amenorrhea: This condition is characterized by the cessation of menstrual cycles due to hypothalamic dysfunction, often triggered by significant stress, excessive exercise, and caloric restriction. The patient's history of recent onset of symptoms after coming off the pill, combined with her lifestyle changes, strongly supports this diagnosis. The normal to low levels of LH and FSH, along with the relatively low oestradiol level, are consistent with hypothalamic amenorrhea.

• Other Likely Diagnoses

  • Polycystic Ovary Syndrome (PCOS): Although the patient's symptoms and some laboratory findings could suggest PCOS, the low testosterone level and low Free Androgen Index (FAI) make this diagnosis less likely. PCOS typically presents with hyperandrogenism, which is not evident in this case.
  • Hyperprolactinemia: The elevated prolactin level could suggest a prolactinoma or other causes of hyperprolactinemia, which can lead to amenorrhea. However, the clinical context and the fact that prolactin levels can be elevated due to stress and other factors make this a less straightforward diagnosis.

• Do Not Miss Diagnoses

  • Pituitary Tumor (including Prolactinoma): Although less likely given the clinical context, a pituitary tumor could explain the elevated prolactin and amenorrhea. It is crucial to investigate this possibility due to the potential serious consequences of missing such a diagnosis.
  • Thyroid Dysfunction: Although not directly indicated by the provided laboratory results, thyroid disorders can cause menstrual irregularities and should be considered, especially given the potential for thyroid issues to be associated with significant morbidity if untreated.

• Rare Diagnoses

  • Premature Ovarian Insufficiency (POI): This condition, formerly known as premature ovarian failure, is characterized by the loss of ovarian function before the age of 40. The patient's FSH level is within the normal range, making this diagnosis less likely, but it should be considered in the differential diagnosis due to its significant implications for fertility and long-term health.
  • Other Endocrine Disorders: Rare endocrine disorders affecting the hypothalamic-pituitary-gonadal axis could also lead to amenorrhea and should be considered if initial evaluations do not lead to a clear diagnosis.