Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (223 page)

   With a normal testosterone level but a low sperm count, the gonadotropins should be measured. If the LH level is normal and the FSH level is high, then the indication is seminiferous tubule damage (leaving testosterone production by the Leydig cells intact).

   With a low or borderline testosterone level and a low sperm count, then LH and FSH levels can distinguish primary from secondary causes of hypogonadism. If the gonadotropins are above normal, the indication is primary hypogonadism. If they are normal or low, then the indication is secondary hypogonadism.

   Table
6-7
summarizes the diagnosis of hypogonadism, and the laboratory differentiation of primary vs secondary causes.

Suggested Readings

Nachtigall LB, Boepple PA, Pralong FP, et al. Adult-onset idiopathic hypogonadotropic hypogonadism—a treatable form of male infertility.
N Engl J Med.
1997;336:410–415.

Smyth CM, Bremner WJ. Klinefelter syndrome.
Arch Intern Med.
1998;158:1309–1314.

Bremner WJ, Vitiello MV, Prinz PN. Loss of circadian rhythmicity in blood testosterone levels with aging in normal men.
J Clin Endocrinol Metab.
1983;56:1278–1281.

Giagulli VA, Kaufman JM, Vermeulen A. Pathogenesis of the decreased androgen levels in obese men.
J Clin Endocrinal Metab.
1994;79:997–1000.

Mingrone G, Greco AV, Giancaterini A, et al. Sex hormone-binding globulin levels and cardiovascular risk factors in morbidly obese subjects before and after weight reduction induced by diet or malabsorptive surgery.
Atherosclerosis.
2002:161:455–462.

Deslypere JP, Vermeulen A. Leydig cell function in normal men: effect of age, life-style, residence, diet, and activity.
J Clin Endocrinol Metab.
1984;59:955–962.

   
DISORDERS OF THE PITUITARY GLAND

HYPOPITUITARISM

   Definition

Hypopituitarism is the deficiency of one or more pituitary hormones resulting from either pituitary or hypothalamic dysfunction. The term panhypopituitarism is used when all the anterior pituitary hormones are absent. When hypothalamic disease is also present, vasopressin deficiency may occur.

   Overview

The prevalence of hypopituitarism is 46 cases per 100,000 individuals. The incidence is approximately 4 cases per 100,000 per year.

   Causes

Pituitary tumors and other neoplastic processes are the most common causes of acquired hypopituitarism.

I.   Pituitary diseases

  1.  Mass lesions. They include pituitary adenomas, cysts, lymphocytic hypophysitis, metastatic cancers, and other lesions.

  2.  Following surgical or radiation treatment of the pituitary

  3.  Infiltrative diseases

a.   Hereditary hemochromatosis in the pituitary is characterized by ion deposition in pituitary cells, which leads to hormonal deficiencies.

b.   Lymphocytic hypophysitis often associates with pregnancy and occurs in the postpartum period. It is initially characterized by lymphocytic infiltration and enlargement of the pituitary and then followed by destruction of the pituitary cells. Affected patients typically present with headaches of an intensity out of proportion to the size of the lesion and hypopituitarism.

  4.  Pituitary infarction (Sheehan syndrome). Typically, the patients have a history of severe postpartum hemorrhage to cause hypotension and require blood transfusions. Severe hypopituitarism can be recognized during the first days or weeks after delivery by the development of lethargy, anorexia, weight loss, and inability to lactate.

  5.  Pituitary apoplexy. Sudden hemorrhage into pituitary gland is called pituitary apoplexy. Hemorrhage often occurs into a pituitary adenoma. It is manifested by sudden onset of headache, cranial nerve defects, visual defects, and hypopituitarism.

  6.  Empty sella syndrome. An empty sella refers to an enlarged sella turcica that is not entirely filled with pituitary tissue.

a.   Primary empty sella is due to a congenital defect in the sellar diaphragm.

b.   Secondary empty sella is due to surgery, radiation treatment, or tumor infarction.

  7.  Genetic defects. Mutations in genes encoding transcription factors necessary for differentiation of anterior pituitary cells have been identified, and they lead to congenital deficiency of one or more pituitary hormones.

II.  Hypothalamic diseases

A.   Mass lesions. These include primary benign tumors, such as craniopharyngiomas, and metastatic malignant tumors, such as lung and breast carcinomas.

B.   Hypothalamic radiation. It is often associated with radiation treatment for brain tumors and nasopharyngeal carcinomas.

C.   Infiltrative diseases. Sarcoidosis and Langerhans cell histiocytosis can cause deficiencies of anterior pituitary hormones.

D.   Infections. The most common etiology is tuberculous meningitis.

E.   Basal skull fracture or head trauma

   Who Should Be Suspected?

Hypopituitarism should be suspected in any patient with midline defects or pituitary and/or hypothalamic masses. Symptoms are mainly secondary to target gland dysfunction (i.e., thyroid, adrenal, gonads) due to deficiency of TSH, ACTH, growth hormone, or gonadotropin but can also be related to local symptoms if a mass is present (i.e., headache, visual disturbances). In pituitary apoplexy, symptoms can be dramatic.