Differential Diagnosis for 61-year-old Man with Low Testosterone, Normal LH, and Normal Prolactin

• Single Most Likely Diagnosis
  • Hypogonadism due to aging or late-onset hypogonadism: This condition is characterized by low testosterone levels, which can occur naturally with aging. The normal LH levels suggest that the issue may not be with the pituitary gland's ability to stimulate the testes but rather with the testes themselves or the impact of aging.
• Other Likely Diagnoses
  • Secondary hypogonadism due to pituitary dysfunction (despite normal LH, as this can fluctuate): Although the LH level is reported as normal, secondary hypogonadism due to pituitary issues should be considered, especially if there's any history suggesting pituitary disease.
  • Testicular dysfunction or failure: Conditions affecting the testes directly, such as orchitis, testicular trauma, or testicular cancer, could lead to low testosterone production.
  • Chronic illness or systemic disease: Certain chronic illnesses, like chronic obstructive pulmonary disease (COPD), liver disease, or renal failure, can lead to hypogonadism.
• Do Not Miss Diagnoses
  • Hemochromatosis: This genetic disorder leads to iron overload, which can cause testicular failure and hypogonadism. It's crucial to diagnose and treat early to prevent long-term damage.
  • Pituitary or hypothalamic tumors (even with normal LH and prolactin, as these can be intermittently elevated or cause dysfunction not reflected in a single blood test): Although prolactin is normal, a tumor could still be present and affecting gonadotropin release.
• Rare Diagnoses
  • Myotonic dystrophy: A genetic disorder that can lead to testicular atrophy and hypogonadism among other systemic symptoms.
  • Klinefelter syndrome (if not previously diagnosed): Although typically diagnosed earlier in life, some cases might not be identified until later, especially if mild.
  • Other genetic disorders affecting testicular function or the hypothalamic-pituitary-gonadal axis.