Hypothyroidism Does Not Directly Cause Rigors
Rigors (shaking chills) are not a typical manifestation of hypothyroidism itself and should prompt investigation for an alternative cause, most commonly infection. While hypothyroidism causes cold intolerance and can lower body temperature, it does not produce the violent shaking episodes characteristic of rigors 1, 2, 3.
Clinical Presentation of Hypothyroidism
The most common symptoms of hypothyroidism include 1, 2, 3:
- Fatigue and lethargy (occurring in 68-83% of patients) 1
- Cold intolerance (a subjective feeling of being cold, not shaking chills) 1, 2, 3
- Weight gain (24-59% of patients) 1
- Dry skin 2, 3
- Constipation 2, 3
- Cognitive impairment including memory loss and difficulty concentrating (45-48%) 1, 4
- Menstrual irregularities (approximately 23%) including oligomenorrhea and menorrhagia 1
- Voice changes 2, 3
Why Rigors Indicate a Different Problem
Rigors represent an acute febrile response characterized by violent shaking and teeth chattering, typically triggered by rapid temperature elevation during bacteremia or severe infection 1, 2. This is fundamentally different from the chronic cold intolerance of hypothyroidism, where patients simply feel cold and may layer clothing but do not experience involuntary shaking episodes 2, 3.
Critical Exception: Myxedema Coma
The one life-threatening scenario where hypothyroidism can present with altered thermoregulation is myxedema coma, which is characterized by 1:
- Hypothermia (not rigors or shaking)
- Hypotension
- Altered mental status
- Mortality rate up to 30% requiring intensive care unit treatment 1
Even in this severe decompensated state, patients develop profound hypothermia rather than rigors 1.
Diagnostic Approach When a Hypothyroid Patient Has Rigors
If a patient with known or suspected hypothyroidism presents with rigors, immediately evaluate for:
- Infection (the most common cause of rigors) - obtain blood cultures, urinalysis, chest imaging as clinically indicated 1
- Sepsis - assess vital signs, lactate, complete blood count 1
- Other febrile illnesses unrelated to thyroid dysfunction 1, 2
Do not attribute rigors to hypothyroidism alone - this represents a dangerous diagnostic error that can delay treatment of serious infection 1, 2.
Thyroid Function Testing Considerations
If evaluating a patient with rigors and suspected hypothyroidism 1, 3, 4:
- Measure TSH and free T4 to confirm thyroid status 1, 3, 4
- Recognize that acute illness can transiently alter thyroid function tests - TSH may be suppressed during severe infection even in hypothyroid patients 5
- Defer thyroid hormone initiation until acute illness resolves unless myxedema coma is diagnosed 5
Common Pitfall
Avoid misattributing rigors to "severe hypothyroidism" - even profoundly hypothyroid patients do not develop rigors as a manifestation of thyroid hormone deficiency 1, 2, 3. The presence of rigors mandates evaluation for infection or other acute illness regardless of thyroid status 1.