In a 63‑year‑old post‑menopausal woman with follicle‑stimulating hormone 5.4 IU/L, luteinizing hormone 2.2 IU/L, testosterone 112 ng/dL, and dehydroepiandrosterone 10 µg/dL, what additional tests should be ordered and what is the differential diagnosis?

Unexpectedly Low Gonadotropins in a Postmenopausal Woman: Diagnostic Approach

This 63-year-old woman has inappropriately low FSH (5.4 IU/L) and LH (2.2 IU/L) for her postmenopausal status, combined with elevated testosterone (112 ng/dL) and low DHEA (10 µg/dL), suggesting either secondary hypogonadism from hypothalamic-pituitary dysfunction or an androgen-secreting tumor suppressing gonadotropins.

Understanding the Hormonal Pattern

The key abnormality here is that FSH and LH are far too low for a woman 14+ years postmenopause. Expected postmenopausal values are FSH >35 IU/L (typically 75+ IU/L) and LH >11 IU/L (typically 37+ IU/L) 1, 2. Her values of FSH 5.4 and LH 2.2 are in the premenopausal range, which is physiologically inappropriate unless:

• Exogenous estrogen or testosterone is suppressing the hypothalamic-pituitary axis 3
• Pituitary dysfunction (hypopituitarism, macroadenoma, or other sellar mass) is present 3
• An androgen-secreting tumor is producing enough testosterone to suppress gonadotropins 4
• Functional suppression from obesity, chronic illness, or medications is occurring 3

The elevated testosterone (112 ng/dL, which is 2-3× the upper limit of normal for postmenopausal women) combined with low DHEA (10 µg/dL, which is low-normal to low for age) creates a pattern inconsistent with simple PCOS or adrenal hyperandrogenism 3, 4.

Immediate Additional Testing Required

First-Line Hormonal Evaluation

• Repeat morning (8 AM) total testosterone by LC-MS/MS to confirm elevation, as immunoassays can be inaccurate 3, 4
• Free testosterone (calculated FAI or equilibrium dialysis) and SHBG to assess bioavailable androgen 3, 4
• Androstenedione (A4) to help localize androgen source (ovarian vs. adrenal) 3, 4
• DHEA-S (not just DHEA) to assess adrenal contribution; levels >600 µg/dL suggest adrenocortical carcinoma 4
• Prolactin to exclude prolactinoma, which can suppress gonadotropins and cause secondary hypogonadism 3, 5
• TSH and free T4 to exclude central hypothyroidism from pituitary dysfunction 3, 5
• 8 AM cortisol or ACTH stimulation test to assess for adrenal insufficiency if pituitary pathology is suspected 3
• IGF-1 to screen for growth hormone deficiency if panhypopituitarism is suspected 3

Imaging Studies

• MRI of the sella with pituitary cuts (with and without contrast) to evaluate for pituitary macroadenoma, microadenoma, hypophysitis, or other sellar/suprasellar masses that could cause hypopituitarism 3
• Pelvic ultrasound or MRI to evaluate for ovarian masses (androgen-secreting tumors such as Sertoli-Leydig cell tumor, thecoma, or hilar cell tumor) 4
• Adrenal CT (non-contrast) to evaluate for adrenal adenoma or carcinoma if DHEA-S is markedly elevated or if testosterone remains unexplained 3, 4

Differential Diagnosis by Likelihood

Most Likely: Pituitary Dysfunction (Secondary Hypogonadism)

• Pituitary macroadenoma (prolactinoma, nonfunctioning adenoma) compressing normal pituitary tissue 3
• Hypophysitis (lymphocytic, autoimmune, or IgG4-related) causing panhypopituitarism 3
• Empty sella syndrome or Sheehan syndrome (though no history of postpartum hemorrhage mentioned) 3
• Pituitary apoplexy or prior pituitary surgery/radiation (history not provided) 3
• Infiltrative disease (sarcoidosis, hemochromatosis, Langerhans cell histiocytosis) 3

The inappropriately low gonadotropins with low-normal to low other pituitary hormones (if present) would confirm this diagnosis 3.

Moderately Likely: Androgen-Secreting Tumor

• Ovarian androgen-secreting tumor (Sertoli-Leydig cell tumor, hilar cell tumor, thecoma) presenting with testosterone >150 ng/dL and rapid-onset virilization 4
• Adrenocortical carcinoma if DHEA-S >600 µg/dL, though current DHEA is low 4

Androgen-secreting tumors typically present with rapid-onset virilization (deepening voice, clitoromegaly, male-pattern baldness, increased muscle mass) and testosterone often >150-200 ng/dL 4. The relatively modest testosterone elevation (112 ng/dL) and absence of severe virilization make this less likely but still possible 4.

Less Likely but Must Exclude

• Exogenous androgen use (testosterone gel, DHEA supplements, anabolic steroids) suppressing endogenous gonadotropins 3, 4
• Functional hypogonadotropic hypogonadism from severe obesity, chronic illness, or medications (opiates, glucocorticoids, GnRH agonists) 3
• Subclinical pituitary dysfunction seen in some postmenopausal women with obesity and higher free estradiol index, though this typically presents with FSH 10-20 IU/L, not 5.4 IU/L 6

Unlikely Given the Pattern

• PCOS is excluded because PCOS requires reproductive-age presentation, and postmenopausal women do not develop new-onset PCOS 3, 4
• Primary ovarian insufficiency (POI) is excluded because POI presents with elevated FSH (>35 IU/L) and LH (>11 IU/L), not low values 1
• Nonclassic congenital adrenal hyperplasia would present with elevated DHEA-S and 17-hydroxyprogesterone, not low DHEA 4

Clinical Red Flags Requiring Urgent Evaluation

• Rapid-onset virilization (deepening voice, clitoromegaly, increased muscle mass) suggests androgen-secreting tumor 4
• Headache, visual field defects, or diplopia suggest pituitary macroadenoma with mass effect 3
• Severe fatigue, weight loss, hypotension, or hyponatremia suggest adrenal insufficiency from panhypopituitarism 3
• Galactorrhea suggests prolactinoma 3, 5

Common Pitfalls to Avoid

• Do not assume menopause based on age alone—FSH and LH must be appropriately elevated (FSH >35 IU/L, LH >11 IU/L) to confirm ovarian failure 1, 7
• Do not rely on a single FSH measurement—FSH fluctuates wildly during perimenopause, but by 14 years postmenopause it should be consistently elevated 7, 8
• Do not use direct immunoassay for free testosterone—it is highly inaccurate in women; use calculated FAI or equilibrium dialysis 3, 4
• Do not overlook exogenous androgen use—specifically ask about testosterone gels, DHEA supplements, or "anti-aging" hormone treatments 4
• Do not delay pituitary MRI—inappropriately low gonadotropins in a postmenopausal woman warrant imaging to exclude a pituitary mass 3

Next Steps in Management

1. Obtain MRI of the sella to evaluate for pituitary pathology 3
2. Repeat testosterone by LC-MS/MS with free testosterone, SHBG, A4, and DHEA-S 3, 4
3. Check prolactin, TSH, free T4, 8 AM cortisol, and IGF-1 to assess for panhypopituitarism 3, 5
4. Perform pelvic ultrasound or MRI if testosterone remains elevated and pituitary imaging is normal 4
5. Consider adrenal CT if DHEA-S is markedly elevated (>600 µg/dL) 3, 4
6. Refer to endocrinology for further evaluation and management of suspected pituitary dysfunction or androgen-secreting tumor 3, 4