MKSAP Quiz: Decreased libido, fatigue
A 32-year-old man is evaluated for decreased libido and fatigue. His symptoms have increased over the last 6 months. Following a physical exam and visual exam, what is the most appropriate diagnostic test to perform next?
A 32-year-old man is evaluated for decreased libido and fatigue. His symptoms have increased over the last 6 months. His medical history is otherwise unremarkable, and he takes no medications.
On physical examination, vital signs are normal. BMI is 26. He has gynecomastia. Visual field acuity testing and testicular examination are normal. Smell is intact.
Laboratory studies:
| Follicle-stimulating hormone | 4 mU/mL (4 U/L) |
| Luteinizing hormone | 5 mU/mL (5 U/L) |
| Prolactin | 100 ng/mL (100 µg/L) |
| Testosterone | 110 ng/dL (3.8 nmol/L) |
Which of the following is the most appropriate diagnostic test to perform next?
A. Karyotype analysis
B. Pituitary MRI
C. Screening for anabolic steroid abuse
D. Serum ferritin measurement
E. Sex hormone-binding globulin measurement
MKSAP Answer and Critique
The correct answer is B. Pituitary MRI. This content is available to MKSAP 18 subscribers as Question 73 in the Endocrinology and Metabolism section. More information about MKSAP is available online.
The most appropriate test for this patient is a pituitary MRI. With a low testosterone level and low serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) concentrations, this patient has secondary hypogonadism. Hyperprolactinemia is the most likely cause of his hypogonadism; hyperprolactinemia leads to secondary hypogonadism through suppression of gonadotropin-releasing hormone synthesis and secretion. This patient is on no medications that might cause hyperprolactinemia. In the absence of a culprit drug, the most likely cause of his hyperprolactinemia is a lactotroph adenoma; therefore a pituitary MRI is indicated.
A karyotype analysis is not indicated in the evaluation of secondary hypogonadism; however, it should be considered in men and women who have primary hypogonadism.
Anabolic steroid use will result in low or normal gonadotropin levels, a low testosterone level, and clinical evidence of hyperandrogenism such as excessive muscle bulk, acne, gynecomastia, and decreased testicular volume. Anabolic steroid abuse, however, would not cause hyperprolactinemia as seen in this patient.
Most patients with hereditary hemochromatosis are diagnosed in the presymptomatic phase when iron test results are abnormal. In patients with symptoms, clinical presentation varies and often includes nonspecific findings such as chronic fatigue, weakness, nonspecific abdominal pain, arthralgia, and elevated liver enzymes. Endocrine organs are commonly affected, and diabetes mellitus, hypothyroidism, and gonadal failure may occur. Laboratory evaluation of hemochromatosis-related gonadal failure most commonly demonstrates a hypogonadotropic state (low LH and FSH levels). While this patient is hypogonadotrophic, he has an elevated prolactin level, and a pituitary MRI is the best next diagnostic test.
Obesity results in decreased concentrations of sex hormone-binding globulin (SHBG); if SHBG is low, free testosterone should be measured in patients with low total testosterone concentrations. This patient does not have obesity and has evidence of secondary hypogonadism (low testosterone level and low serum LH and FSH concentrations), making determination of SHBG concentration unnecessary.
Key Point
- Secondary hypogonadism is characterized by low testosterone level and low or inappropriately normal serum luteinizing hormone and follicle-stimulating hormone concentrations; MRI of the pituitary is typically performed to evaluate secondary hypogonadism in the absence of obvious reversible causes such as drugs.