Differential Diagnosis of Shortened Menstrual Interval (Polymenorrhea)

Primary Endocrine Differentials

Polycystic ovary syndrome (PCOS) affects 4-6% of women and is the most common cause of menstrual cycle irregularities, including shortened cycles, characterized by elevated androgens, irregular or absent periods, and polycystic ovarian morphology on ultrasound, with laboratory findings typically showing an LH:FSH ratio >2 3, 2
The American College of Obstetricians and Gynecologists recommends looking for associated hirsutism, truncal obesity, and acne in patients with PCOS 1
Thyroid dysfunction, including both hypothyroidism and hyperthyroidism, disrupts the hypothalamic-pituitary-ovarian axis and can cause shortened menstrual intervals, with initial workup including serum TSH levels 2, 3
Hyperprolactinemia accounts for approximately 20% of secondary amenorrhea cases but can also present with irregular shortened cycles, with prolactin levels >20 μg/L considered abnormal, and galactorrhea being a common symptom 1, 2

Anovulatory cycles are the most common mechanism underlying polymenorrhea, resulting in irregular endometrial shedding, with mid-luteal progesterone <6 nmol/L indicating anovulation 1
Common causes of anovulation include PCOS, functional hypothalamic amenorrhea, and hyperprolactinemia 2

Inconsistent or incorrect use of hormonal contraceptives is a major cause of menstrual irregularities, including shortened intervals, with missing pills or extending the hormone-free interval disrupting the cycle 3
Copper IUDs commonly cause irregular bleeding patterns, especially in the first 3-6 months, with IUD displacement or malposition causing abnormal bleeding 4

Advanced liver disease causes menstrual irregularities in >25% of women through altered estrogen metabolism 2
Von Willebrand disease is present in up to 20% of women with heavy menstrual bleeding and can present with shortened cycles, with platelet dysfunction or thrombocytopenia being considered 4
Women with epilepsy have unusually high rates of reproductive endocrine disorders, including PCOS, with anovulatory cycles associated with higher seizure frequencies 1, 3

The initial evaluation should include a pregnancy test to exclude pregnancy, with documentation of menstrual patterns using a chart for at least 6 months, and cycles <23 days defined as polymenorrhea 3, 1
Laboratory workup should include measurement of serum FSH, LH, prolactin, and TSH levels, with LH and FSH measured based on an average of three estimations taken 20 minutes apart between day 3 and 6 of the cycle 3, 1

Persistent anovulatory cycles can lead to decreased bone mineral density and increased osteoporosis risk due to hypoestrogenic states, with women with menstrual disorders having a higher risk of developing hypertension and cardiometabolic risk factors 3, 2
Reproductive endocrine disorders are associated with higher rates of infertility, with irregular menstruation associated with metabolic syndrome, coronary heart disease, and type 2 diabetes 1, 2