Heat Illnesses and Heat Stroke - Differential Diagnosis Framework



Heat Cramps:

 • Muscle pain or spasm - legs, arms or abdomen

 • Due to:

	- Strenuous exercise in the heat

	- Dehydration

	- Loss of sodium/Potassium

	- Extreme environmental conditions

	- Neurogenic fatigue



Heat Rash:

 • Small red bumps/blisters on the skin

 • Areas that stay wet from sweat



Heat Injury:

 • Exertional heat illness → Hypernatremia & end organ damage without neuro manifestations

 • Organ involvement: Muscles, Kidneys, Liver

 • Labs:

	- Metabolic acidosis

	- Rhabdomyolysis

	- AKI

	- Liver failure



Heat Syncope / Exercise Associated Collapse:

 • Pathophysiology: Volume depletion → Decreased vasomotor tone → Postural hypotension → Syncope

 • Signs/Symptoms:

	- Lightheadedness

	- Tunnel vision

	- Pale and sweaty skin

	- Decreased pulse rate

	- Core temp normal/mildly elevated



Heat Exhaustion:

 • Inability to maintain adequate cardiac output due to strenuous physical exercise and environmental heat stress

 • Criteria:

	- Athlete - difficulty continuing with exercise

	- Core body temp 101-104 degrees F

	- No significant CNS dysfunction

 • Other manifestations:

	- Tachycardia & hypotension

	- Extreme weakness

	- Dehydration and electrolyte losses

	- Ataxia and coordination problems - syncope/lightheadedness

	- Profuse sweating, pallor, “prickly heat” sensations

	- Headache

	- Abdominal cramps, N/V, diarrhea

	- Persistent muscle cramps



Exertional Heat Stroke: EMERGENCY

 • Multi-system illness:

	1. CNS dysfunction (encephalopathy)

	2. Organ and tissue damage (AKI, Liver injury, Rhabdomyolysis, Thermal cardiomyopathy, ARDS, DIC)

	3. High body temperatures

 • Criteria:

	- Core temp > 104 F

	- CNS dysfunction:

		• Disorientation, Headache, Irrational behavior, Irritability, Emotional instability, Confusion, Altered consciousness, Coma/seizure

 • Other Findings:

	- Tachycardia, Hyperventilation, Dizziness, Nausea, Vomiting, Diarrhea, Weakness, Profuse sweating, Dehydration, Dry mouth, Thirst, Muscle cramps, Loss of muscle function, Ataxia

 • Lab Findings:

	- Mild coagulopathy

	- Possible DIC

	- Mild lactic acidosis

	- CPK elevation

	- Hypoglycemia

	- Hypocalcemia

	- Hyperkalemia



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