Differential diagnoses in heat-related illness

A patient with altered mental state in a hot environment has heat stroke until proven otherwise. Immediate cooling should be started in these patients empirically while differential diagnoses are considered.

However, an elevated core body temperature can be the result of other conditions. Consider other causes of elevated body temperature, which can co-exist with heat-related illness, particularly in athletes. Other causes of an elevated core body temperature include:

• sepsis—a common cause of elevated body temperature with an associated high morbidity and mortality; it must be excluded in all patients with suspected heat stroke
• neuroleptic malignant syndrome (NMS)—hyperthermia, muscular rigidity, altered mental state and autonomic lability
• drug toxicity, including illicit drugs (eg serotonergic toxidrome, amfetamines such as ‘ice’)
• malignant hyperthermia—a genetic disorder in which specific triggers (anaesthetic drugs, most commonly) stimulate overwhelming intracellular calcium release, producing profound muscle contraction and disordered metabolism¹; see the Malignant Hyperthermia Group of Australia and New Zealand website for more information.

Also consider other causes of exertion-related changes in consciousness:

• postexertional collapse (exercise-associated collapse)—a diagnosis of exclusion; transient hypotension is thought to be caused by venous pooling after exerciseAsplund, 2011
• severe exercise-associated hyponatraemia usually in individuals who have drunk large amounts of water or hypotonic sports drinks while sweating profusely, are hypervolaemic and have high urine output²Bennett, 2020
• hypoglycaemia
• hyperglycaemia.