OBESITY

The differential diagnosis of obesity, like that of weight loss, is best developed using physiology because most cases of obesity are caused by an absolute increased intake of calories or a relative increased intake of calories over output of energy. Fluid retention may also be associated with weight gain.


OBESITY

Increased intake of calories. This type of obesity is due to an increased appetite.
Caused by: idiopathic obesity, psychogenic obesity, hypothalamic obesity (due to pituitary tumors and other lesions affecting the hypothalamus), islet cell adenomas and carcinomas (causing hypoglycemia and, consequently, a big appetite), early stages of diabetes mellitus when functional hypoglycemia is common, Cushing syndrome and exogenous corticosteroids (which increase appetite), and alcoholism, which stimulates the appetite but which also adds calories in the alcohol (up to 250 cal per cocktail).


Decreased output of energy.
Causes: Hypothyroidism and possibly hypogonadism (such as Klinefelter syndrome), where the motivation to work or exercise may be impaired. Mild pituitary insufficiency (as in Sheehan or Fröhlich syndrome) may also cause obesity by this mechanism. This type of obesity may be occupational (e.g., white collar workers) or environmental (i.e., watching television all day).

“Obesity” due to fluid retention. This increase is in reality an increase in weight from fluid retention. Inappropriate ADH syndromes such as those that occur in carcinoma of the lung, hypothalamic lesions, and drugs are the most important obscure causes. CHF, nephrosis, cirrhosis, beriberi, and myxedema rank as significant among the obvious causes.

Miscellaneous causes. Heredity is a cause of obesity, but the physiologic mechanism is uncertain.

Patients who fail to lose weight on a strict diet may require hospitalization with observation. If they still fail to lose weight, a complete endocrine workup would seem to be indicated.

thyroid function studies may be worthwhile.
48-hour fast with glucose monitoring (insulinoma)
Plasma insulin (insulinoma)
C-peptide (insulinoma)
Serum cortisol (Cushing syndrome)
Dexamethasone suppression test (Cushing syndrome)
Pelvic sonogram (polycystic ovary)
Chromosomal analysis (Klinefelter syndrome)
Psychiatry consult