A 32-year-old woman presents to the office with complaints of missed period for the last two months. She uses a combined oral contraceptive, which she has taken regularly with no missed doses for the past 6 years. She states that she has regular menstruation every 28 days with 4 days of moderate bleeding, but that she missed her period this month and last month. She denies any other complaints or conditions other than missed periods. Past medical history is significant only for onychomycosis treatment 6 weeks ago, treated with a prescription of oral griseofulvin for 4 months duration. Family history is significant for aortic dissection in her father at age 52 years. She does not drink alcohol, smoke cigarettes, or use illicit drugs. She runs 2 miles 3 days a week for exercise. Current medications only include griseofulvin. Vital signs are temperature 37.2° C (98.9° F), blood pressure 120/80 mm Hg, pulse 84 beats/min, respirations 16/min, and oxygen saturation 98% on room air. She is 5’7” and weighs 145 lbs (66 kg). Physical examination shows no abnormalities. Her laboratory results are:
Thyroid stimulating hormone (TSH) 2.0 uU/mL
Free T4 10 mcg/dl
Follicle stimulating hormone (FSH) 0.1 IU/L
Leutinizing hormone (LH) 0.8 IU/L
Prolactin 6 ng/ml
bHCG 250 mIU/mL
Which of the following is the most likely cause of the patients missed menstrual periods?
The correct answer is:
D) Griseofulvin
This patient is pregnant, as evidenced by the elevated bHCG. Griseofulvin is a powerful cytochrome P4350 inducer and can cause estrogen to be quickly metabolized. This can disrupt the protection measures that oral contraceptive pills provide in terms of contraceptive control.
Answer choice A: Adenomyosis, is incorrect. Adenomyosis is a condition where the endometrial tissue grows into the muscular wall of the uterus, causing the uterus to thicken. This generally causes heavy bleeding and clots, not amenorrhea.
Answer choice B: Anovulation, is incorrect. Anovulation is a lack or absence of ovulation. It is a common cause of infertility in polycystic ovary syndrome (PCOS) and overweight women. Anovulation is often the result of an imbalance of leutinizing hormone (LH) and follicle stimulating hormone (FSH). While this is a cause of amenorrhea, this patient’s levels of LH and FSH suggest pregnancy instead.
Answer choice C: Exercise-induced amenorrhea, is incorrect. Exercise-induced amenorrhea is caused by excess amounts of exercise and a very low body mass index (BMI), which this patient does not have.
Answer choice E: Pituitary adenoma, is incorrect. Pituitary adenomas can cause anovulation through excess prolactin levels, generally 150-200 6 ng/ml, which this patient does not have.
Key Learning Point
Inducers of cytochrome p450, such as griseofulvin, can make other medications less effective, or ineffective. Other inducers of cytochrome p450 include carbamazepine, phenobarbital, phenytoin, rifampin, ethanol, isoniazid, tobacco, and St. Johns Wort.
