What is the likely cause of secondary amenorrhea (absence of menstruation) in a 22-year-old female with a history of irregular menstrual cycles (oligomenorrhea), given her normal Follicle-Stimulating Hormone (FSH) level, mildly elevated Prolactin level, and negative Human Papillomavirus (HPV) test, and should she be referred to a Gynecologist (GYN) for further evaluation?

Differential Diagnosis for a 22-year-old Female with Missed Periods

Single Most Likely Diagnosis

• Polycystic Ovary Syndrome (PCOS): Given the patient's history of irregular periods and the presence of amenorrhea (missed periods since December), PCOS is a strong consideration. The normal FSH level and slightly elevated prolactin level do not strongly argue against this diagnosis, as PCOS can present with a wide range of hormonal profiles.

Other Likely Diagnoses

• Hypothalamic Amenorrhea: This condition, characterized by the cessation of menstrual cycles due to hypothalamic dysfunction, could be a consideration given the patient's stress levels, weight changes, or excessive exercise, although these factors are not mentioned.
• Thyroid Dysfunction: Although not directly indicated by the information provided, thyroid issues can cause menstrual irregularities. A TSH level would be helpful to rule out hypothyroidism or hyperthyroidism.
• Pituitary Adenoma: The slightly elevated prolactin level could suggest a pituitary adenoma, but this would typically be associated with higher prolactin levels. Further evaluation with an MRI might be considered if prolactin levels were significantly higher or if other symptoms were present.

Do Not Miss Diagnoses

• Pregnancy: Although the patient has a negative pregnancy test, it's crucial to ensure that this result is accurate, especially if there's any chance the test was performed too early or if the patient could have become pregnant since the test.
• Ovarian Failure/Premature Ovarian Insufficiency: Although less likely given the patient's age and FSH level, this is a critical diagnosis not to miss due to its implications for fertility and long-term health.
• Androgen-Secreting Tumors: These are rare but can cause amenorrhea and should be considered if there are signs of virilization or significantly elevated androgen levels.

Rare Diagnoses

• Asherman’s Syndrome: A condition characterized by the formation of adhesions in the uterus, which can lead to amenorrhea. This typically follows uterine surgery or infection.
• Genetic Disorders: Such as Turner syndrome or other genetic conditions that can affect menstrual cycles, though these would likely have been identified earlier in life.

Further Workup or Treatment

Given the information, further workup could include:

• Thyroid function tests (TSH, free T4) to rule out thyroid dysfunction.
• Androgen level testing (e.g., testosterone) if PCOS is suspected.
• Pelvic ultrasound to evaluate ovarian morphology and rule out other pelvic pathology.
• Consider referral to a gynecologist or endocrinologist for further evaluation and management, especially if the diagnosis is unclear or if specialist input is needed for treatment.

Reason to Refer to GYN

Referral to a gynecologist might be considered for:

• Further evaluation of amenorrhea, especially if the cause is unclear after initial workup.
• Management of PCOS or other hormonal imbalances, which may require specialized care.
• Discussion of fertility preservation options if premature ovarian insufficiency is diagnosed.
• Performance of a pelvic exam, which was not mentioned, to assess for any anatomical abnormalities.