Interpret the LHRH (luteinizing hormone‑releasing hormone) (GnRH) stimulation test results—baseline FSH (follicle‑stimulating hormone) <1.0 IU/L, FSH 1.3 IU/L at 20 min, 1.5 IU/L at 60 min; baseline LH (luteinizing hormone) 1.9 IU/L, LH 22.8 IU/L at 20 min, 19.1 IU/L at 60 min—in the context of secondary hypogonadism?

LHRH Stimulation Test Interpretation: Secondary Hypogonadism

Primary Interpretation

These results demonstrate a preserved pituitary response to GnRH stimulation, which argues AGAINST severe secondary (hypothalamic) hypogonadism and instead suggests either functional hypothalamic amenorrhea (FHA) with polycystic ovarian morphology or early/partial hypothalamic dysfunction. 1, 2

Key Findings Analysis

FSH Response Pattern

• Baseline FSH <1.0 IU/L is markedly suppressed and falls below the diagnostic threshold of 1.2 IU/L that confirms hypogonadotropic hypogonadism in males 2
• The FSH rise from <1.0 to 1.5 IU/L at 60 minutes represents only a 0.5 IU/L increment, which is blunted compared to normal responses 2
• In functional hypothalamic amenorrhea (FHA), FSH levels are characteristically lower than in normal cycling women, and this pattern is consistent with that diagnosis 1

LH Response Pattern

• Baseline LH of 1.9 IU/L is low-normal but the robust rise to 22.8 IU/L at 20 minutes demonstrates intact pituitary gonadotroph function 1, 2
• The peak LH of 22.8 IU/L is significantly higher than typical severe hypogonadotropic hypogonadism (where peak responses are typically <5.8 IU/L) but lower than PCOS (where stimulated LH averages 35.48 ± 31.4 IU/L) 1, 2
• In FHA with polycystic ovarian morphology (FHA-PCOM), stimulated LH levels average 17.2 ± 13.4 IU/L, and this patient's response of 22.8 IU/L falls within this range 1

Diagnostic Implications

This Pattern Indicates:

• Functional hypothalamic suppression rather than organic pituitary/hypothalamic disease because the pituitary retains the ability to respond vigorously to exogenous GnRH 1, 3
• The dissociation between robust LH response and blunted FSH response suggests altered GnRH pulse frequency characteristic of functional disorders 4
• Slow GnRH pulse frequency (as occurs in FHA) favors FSH secretion over LH, but the overall suppression of the GnRH pulse generator results in low baseline levels of both 1, 4

What This Rules Out:

• Severe/complete hypogonadotropic hypogonadism is excluded because peak LH >5.8 IU/L has high specificity for preserved gonadotroph function 2
• Primary pituitary failure is excluded because the pituitary demonstrates preserved synthetic capacity and responsiveness 5, 3
• Organic hypothalamic lesions (tumors, infiltrative disease) are less likely given the preserved pituitary response, though imaging may still be warranted clinically 5

Clinical Context Required

Essential Additional Information Needed:

• Clinical history of stress, excessive exercise, weight loss, or eating disorders that characterize FHA 1
• Menstrual pattern documentation: oligomenorrhea vs. amenorrhea duration 1
• Pelvic ultrasound findings: presence of polycystic ovarian morphology (>10 peripheral follicles 2-8mm) would support FHA-PCOM diagnosis 1
• Baseline testosterone and SHBG levels: modest testosterone elevation with low SHBG suggests FHA-PCOM rather than classic PCOS 1
• BMI and nutritional status: low BMI supports FHA diagnosis 1

Differential Diagnosis Considerations:

• FHA with PCOM (most likely): Low baseline gonadotropins with preserved pituitary response, stimulated LH in the 17-23 IU/L range, and clinical context of functional suppression 1
• Early/partial hypothalamic dysfunction: Baseline FSH <1.2 IU/L suggests some degree of hypothalamic suppression, but the robust LH response indicates this is not complete 2
• PCOS with hypothalamic overlay: Less likely because true PCOS shows higher stimulated LH (>35 IU/L) and baseline LH:FSH ratio >2 1, 6

Critical Pitfalls to Avoid

• Do not diagnose complete hypogonadotropic hypogonadism based solely on low baseline FSH when the stimulated response is preserved 2, 3
• Do not confuse FHA-PCOM with PCOS: FHA-PCOM shows lower stimulated LH responses and both baseline gonadotropins are suppressed (often both <2 IU/L in true hypothalamic hypogonadism) 1
• Timing matters: Ensure this test was not performed while on hormonal contraception, which would suppress the entire axis and invalidate results 6
• Do not assume irreversibility: Functional hypothalamic suppression is potentially reversible with treatment of underlying causes (nutritional rehabilitation, stress reduction, exercise modification) 1, 3

Recommended Next Steps

• Obtain pelvic ultrasound to assess for polycystic ovarian morphology 1
• Measure baseline testosterone, SHBG, and AMH to differentiate FHA-PCOM from PCOS 1
• Assess for typical FHA triggers: detailed history of exercise volume, dietary patterns, psychological stressors, and weight changes 1
• Consider MRI of pituitary/hypothalamus only if clinical features suggest organic disease (headaches, visual changes, other pituitary hormone deficiencies) 5
• If fertility desired and FHA confirmed, pulsatile GnRH therapy is the physiologic treatment of choice and would be expected to restore ovulation given the preserved pituitary response demonstrated here 1, 3