Heat intolerance refers to the inability to withstand high temperatures or to maintain a comfortable body temperature This symptom produces a continuous feeling of being overheated and, at times, profuse diaphoresis
It usually develops gradually and is chronic.
Most cases of heat intolerance result from thyrotoxicosis. With this disorder, excess thyroid hormone stimulates peripheral tissues, increasing basal metabolism and producing excess heat. Although rare, hypothalamic disease may also cause intolerance to heat and cold.
Ask the patient when he first noticed his heat intolerance. Did he gradually use fewer blankets at night? Does he have to turn up the air conditioning to keep cool? Is it hard for him to adjust to warm weather? Does he sweat in a hot environment? Find out if his appetite or weight has changed. Also, ask about unusual nervousness or other personality changes. Then take a drug history, especially noting the use of amphetamines or amphetamine-like drugs. Ask the patient if he takes a thyroid drug. If so, what’s the daily dose? When did he last take it?
As you begin the examination, notice how much clothing the patient is wearing. After taking his vital signs, inspect his skin for flushing and diaphoresis. Also, note tremors and lid lag.
With hypothalamic disease, body temperature fluctuates dramatically, causing alternating heat and cold intolerance
Related features include amenorrhea, disturbed sleep patterns, increased thirst and urination, increased appetite with weight gain, impaired visual acuity, a headache, and personality changes, such as bursts of rage or laughter Common causes of hypothalamic disease are pituitary adenoma and hypothalamic and pineal tumors.
A classic symptom of thyrotoxicosis, heat intolerance may be accompanied by an enlarged thyroid, nervousness, weight loss despite increased appetite, diaphoresis, diarrhea, tremor, and palpitations Although exophthalmos is characteristic, many patients don’t display this sign
Associated findings may affect virtually every body system. Some common findings include irritability, difficulty concentrating, mood swings, insomnia, muscle weakness, fatigue, lid lag, tachycardia, full and bounding pulse, a widened pulse pressure, dyspnea, amenorrhea, and gynecomastia. Typically, the patient’s skin is warm and flushed; premature graying and alopecia occur in both sexes.
Amphetamines, amphetamine-like appetite suppressants, and excessive doses of thyroid hormone may cause heat intolerance Anticholinergics may interfere with sweating, resulting in heat intolerance.
Adjust the room temperature to make the patient comfortable
If the patient is diaphoretic, change his clothing and bed linens as necessary, and encourage him to drink lots of fluids.
Rarely, maternal thyrotoxicosis may be passed to the neonate, resulting in heat intolerance More commonly, acquired thyrotoxicosis appears between ages 12 and 14, although this too is infrequent
Dehydration may also make a child sensitive to heat.
Read excerpts from these other book chapters related to Heat intolerance:
Copyright Details: Handbook of Signs & Symptoms (Third Edition), Copyright © 2008 Williams & Wilkins.
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More About This Book:
Title: Handbook of Signs & Symptoms (Third Edition) Authors: Springhouse Publisher: Lippincott Williams & Wilkins Copyright: 2006 ISBN: 1-58255-402-1 
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