Laboratory Studies
The hallmark of endocrine disorders is an abnormal serum level of either a particular hormone or the entire spectrum of associated hormones, such as in anterior hypopituitarism (panhypopituitarism).
Serial hormone assays may be used to determine the secretory pattern and to assess the hypothalamic regulation of pituitary function. All patients with traumatic brain injury (TBI) should undergo a baseline hormone evaluation at the time of hospital or intensive care unit (ICU) discharge, as well as at 3 months and 12 months post-TBI. The endocrinologist's workup may include provocative testing. Confirmatory testing of growth hormone (GH) deficiency is by assay of IGF-I. A low level of IGF-I in the absence of malnutrition is indicative of severe GH deficiency; however, aging or other factors (eg, liver disease, chronic renal disease, obesity, diabetes mellitus) can also cause a low level of IGF-I.
Careful clinical assessment of patients who have sustained TBI and who develop unexplained lethargy, generalized weakness, or anorexia should include an endocrine evaluation. Endocrine problems interfere with the progress of rehabilitation and are detrimental to the rehabilitation outcome if not recognized and treated promptly.
Laboratory/clinical screening studies of pituitary function include the following:
-
GH - Height, weight, and bone age (< 18 y)
-
IGF-I (0900)
-
Thyrotropin - Free T4 and T3 by radioimmunoassay (0900)
-
Corticotropin - Serum cortisol (0900 h)
-
Gonadotropins - Serum estradiol or testosterone (0900)
-
Prolactin - Serum prolactin
-
ADH - Serum/urine sodium, serum/urine osmolalities, and urine output
A study by Salomón-Estébanez et al indicated that children who have suffered mild to moderate TBI may not require routine evaluation for endocrine dysfunction. In the study, 36 pediatric patients, all of whom had suffered skull fracture or intracranial hemorrhage, including 36.6% who had sustained moderate to severe TBI, were assessed for pituitary dysfunction after a mean postinjury period of 3.3 years (with a mean age at assessment of 7.2 years). No pituitary dysfunction was found in these patients at follow-up, including in 4 patients with low serum IGF-I levels and two patients in whom serum cortisol levels were low and plasma adrenocorticotropic hormone (ACTH) levels were inappropriately normal. [35]
Imaging Studies
See the list below:
-
Cranial magnetic resonance imaging (MRI) provides the most specific cross-sectional views of the hypothalamus and pituitary gland. [36] The diagnosis and treatment of endocrine complications following traumatic brain injury (TBI) are based on clinical findings and laboratory studies of overall pituitary hormonal regulation and of each endocrine gland.
-
Effects of hyponatremia on the brain and adaptive responses. Within minutes after the development of hypotonicity, water gain causes swelling of the brain and a decrease in osmolality of the brain. Partial restoration of brain volume occurs within a few hours as a result of cellular loss of electrolytes (rapid adaptation). The normalization of brain volume is completed within several days through loss of organic osmolytes from brain cells (slow adaptation). Low osmolality in the brain persists despite the normalization of brain volume. Proper correction of hypotonicity reestablishes normal osmolality without risking damage to the brain. Overly aggressive correction of hyponatremia can lead to irreversible brain damage.
Tables
Formula* |
|
Clinical Use |
Change in serum Na+ = |
Infusate Na+ — serum Na+ —————————— total body water +1 |
Estimate the effect of 1 L on any infusate serum Na+ |
Change in serum Na+ = |
(Infusate Na+ + infusate K+)—serum Na+ ———————————————— total body water +1 |
Estimate the effect of 1 L of any infusate containing Na+ and K+ on serum Na+ |
|
|
|
Infusate |
Infusate Na+ |
Extracellular—Fluid Distribution |
|
mmol/L |
% |
5% sodium chloride in water |
855 |
100† |
3% sodium chloride in water |
515 |
100† |
0.9% sodium chloride in water |
154 |
100 |
Ringer lactate solution |
130 |
97 |
0.45% sodium chloride in water |
77 |
73 |
0.2% sodium chloride in 5% dextrose in water |
34 |
55 |
5% dextrose in water |
0 |
40 |
*The number in formula 1 is a simplification of the expression (infusate Na+ —serum Na+) X 1 liter, with the value yielded by the equation in mmol/L. The estimated total body water (in liters) is calculated as a fraction of body weight. The fraction is 0.6 in children; 0.6 and 0.5 in nonelderly men and women, respectively; and 0.5 and 0.45 in elderly men and women, respectively.†In addition to its complete distribution in the extracellular compartment, this infusate induces osmotic removal of water from the intracellular compartment. |
||
