A man was working in a field and he suddenly collapsed on a hot summer afternoon. On examination, there were no physical signs of dehydration. His serum electrolyte level was normal. The doctor found that the body temperature was 106 degrees Fahrenheit. Which of the following symptoms is least likely to be seen in this patient?

Explanation

## Correct Answer: D. Sweating This patient presents with classic **heat stroke** (core temperature >40.5°C / 104.9°F), not heat exhaustion. The discriminating feature is the absence of sweating despite extreme hyperthermia. In heat stroke, the body's thermoregulatory centre in the hypothalamus becomes overwhelmed and fails, leading to **cessation of sweating** — a hallmark finding that distinguishes heat stroke from heat exhaustion. Heat exhaustion presents with profuse sweating, normal mental status, and mild temperature elevation; heat stroke presents with high fever, altered mental status, and **dry skin** (anhidrosis). The patient's normal serum electrolytes and absence of clinical dehydration signs further support heat stroke rather than heat exhaustion, as the latter would show electrolyte derangements. The core temperature of 106°F (41.1°C) exceeds the threshold for thermoregulatory failure. In Indian summer conditions, heat stroke is a medical emergency with mortality rates of 10–50% if untreated. The pathophysiology involves direct thermal injury to the CNS, coagulation cascade activation, and multi-organ dysfunction. Sweating is therefore the **least likely** symptom because the thermoregulatory mechanism is fundamentally broken in heat stroke. ## Why the other options are wrong **A. Hot skin** — This is a cardinal sign of heat stroke. The body's inability to dissipate heat results in extremely elevated core temperature manifesting as hot, dry skin. The absence of sweating means no evaporative cooling occurs, so the skin remains hot to touch. This is one of the most consistent clinical findings in heat stroke and is expected in this patient. **B. Disorientation** — CNS involvement is a defining feature of heat stroke. Temperatures >40.5°C cause direct thermal injury to the hypothalamus and cerebral cortex, leading to confusion, delirium, seizures, or coma. The patient's altered mental status (disorientation) is a key diagnostic criterion for heat stroke and would definitely be present at 106°F core temperature. **C. Hypotension** — Heat stroke causes profound cardiovascular instability due to peripheral vasodilation, direct myocardial injury, and hypovolemia from fluid shifts. Hypotension is a common complication reflecting circulatory collapse and is frequently seen in severe heat stroke cases, especially in Indian summer presentations with delayed recognition. ## High-Yield Facts - **Heat stroke** is defined as core temperature >40.5°C (104.9°F) with CNS dysfunction; **anhidrosis (absent sweating)** is the pathognomonic sign due to thermoregulatory centre failure. - **Heat exhaustion** (the precursor) presents with profuse sweating, normal mental status, and temperature <40°C; sweating is preserved because the thermoregulatory centre is still functional. - **Exertional heat stroke** (outdoor, young, active) vs **non-exertional heat stroke** (elderly, sedentary, drugs like anticholinergics) — both present with anhidrosis but exertional is more common in Indian agricultural workers. - **SIRS criteria** in heat stroke: fever, tachycardia, tachypnea, altered mental status; **DIC** (disseminated intravascular coagulation) is a major complication causing bleeding and multi-organ failure. - **Immediate management**: rapid cooling (ice water immersion, cold IV fluids, evaporative cooling), aggressive fluid resuscitation, and ICU monitoring for rhabdomyolysis and acute kidney injury. ## Mnemonics **Heat Stroke vs Heat Exhaustion: DRY vs WET** **Heat Stroke** = **DRY** skin (anhidrosis), altered mental status, temperature >40.5°C, thermoregulatory failure. **Heat Exhaustion** = **WET** skin (profuse sweating), normal mentation, temperature <40°C, thermoregulation intact. Use this when distinguishing between the two in summer collapse cases. **Heat Stroke Complications: CRASH** **C**erebral edema, **R**habdomyolysis, **A**cute kidney injury, **S**IRS/Sepsis, **H**ypovolemia/Hypotension. Helps recall the multi-system involvement and why heat stroke is a medical emergency. ## NBE Trap NBE pairs "normal electrolytes" with heat stroke to trick students into thinking only heat exhaustion causes electrolyte derangement. However, heat stroke can present with normal initial electrolytes if the patient collapsed acutely; electrolyte abnormalities develop later with rhabdomyolysis and renal failure. The key discriminator is the **absence of sweating**, not electrolyte status. ## Clinical Pearl In Indian summer, heat stroke is often missed because patients present to rural health centres where core temperature measurement is unavailable. The **absence of sweating** in a collapsed agricultural worker on a hot day is the bedside red flag that should immediately trigger suspicion of heat stroke and emergency cooling measures — delaying treatment by even 30 minutes increases mortality significantly. _Reference: Robbins & Cotran Pathologic Basis of Disease, Ch. 9 (Environmental and Nutritional Pathology); Parikh's Textbook of Medical Jurisprudence & Toxicology (Heat-related deaths); Harrison's Principles of Internal Medicine, Ch. 471 (Hypothermia and Heat-related Illnesses)_