Differentials
Nonmalignant hyperthermia rhabdomyolysis
SIGNS / SYMPTOMS
Electrocardiographic abnormality (peaked T waves and/or bradycardia) evolves into ventricular fibrillation prior to the elevation of carbon dioxide tension in blood or end-expiratory gas. With decreasing cardiac output, carbon dioxide tension will decrease in expiratory gas.[51]
INVESTIGATIONS
Blood gas and electrolyte measurement shows acidemia and hyperkalemia.
Resolves with treatment of hyperkalemia with calcium.
Muscle histopathology reveals primary muscle pathology.
Genetic diagnosis of muscle disease, such as dystrophinopathy.
Muscle disuse atrophy
SIGNS / SYMPTOMS
A history of immobility or neuromuscular injury and exposure to succinylcholine is usually present.[79]
Electrocardiographic abnormality (peaked T waves and/or bradycardia) evolves into ventricular fibrillation prior to elevation of carbon dioxide tension in blood or end-expiratory gas.
INVESTIGATIONS
Extreme hyperkalemia can occur after the administration of succinylcholine to a patient with muscle disuse atrophy.
Respiratory and metabolic acidosis are usually more marked than hyperkalemia in a patient experiencing an early malignant hyperthermia crisis.
Resolves with treatment of hyperkalemia with calcium.
Muscle histopathology may have signs of denervation or necrosis.
Myotonia
SIGNS / SYMPTOMS
Muscle stiffness occurs without a markedly increased metabolism.
INVESTIGATIONS
Electromyography shows characteristic changes.
In some cases genetic testing can be used to diagnose myotonia.
Sepsis
SIGNS / SYMPTOMS
Sepsis-induced hyperpyrexia may be suppressed by volatile anesthetics, and present more profoundly in the post-anesthetic period. However, unlike malignant hyperthermia, it does respond to antipyretic therapy such as acetaminophen.[7]
INVESTIGATIONS
Responds to antipyretic drugs. The temperature often decreases after acetaminophen in the presence of infection.
Culture of blood, urine, or other material reveals a source of infection.
White cell count is elevated.
Complications of laparoscopic surgery
SIGNS / SYMPTOMS
Increased airway pressure is required to maintain minute ventilation but muscle tone is normal.
Breath sounds are normal.
Crepitus may be present if carbon dioxide has escaped from the body cavity into the subdermal space. This can also happen if carbon dioxide escapes onto a second cavity, for instance in capnothorax. This increases carbon dioxide absorption and apparent carbon dioxide production, but is not associated with increased temperature, heart rate, or higher oxygen consumption.
A useful rule of thumb is that if the baseline minute ventilation needs to be more than doubled, then either carbon dioxide is migrating beyond the operative cavity or metabolism is increased.
INVESTIGATIONS
No differentiating tests.
Allergic reaction
SIGNS / SYMPTOMS
Airway edema, wheezing, and urticaria may be present.
INVESTIGATIONS
Responds to epinephrine, antihistamines, and corticosteroids.
No response to dantrolene.
Tryptase and immunoglobulins elevated in blood.
Skin testing or blood testing identifies allergen.
Serotonin syndrome
SIGNS / SYMPTOMS
Progression to critical temperature and multiorgan system failure may be slower than during malignnat hyperthermia.
Triggered by serotonergic drugs rather than inhalation anesthetics.[61][80][81][82]
Patients prescribed more than one serotonergic agent are at increased risk (e.g., monoamine oxidase inhibitors may enhance the serotonergic effect of meperidine, resulting in serotonin syndrome).[61][82]
INVESTIGATIONS
Absence of other causes of temperature elevation and rigidity and presence of the drug in the plasma.
Neuroleptic malignant syndrome
SIGNS / SYMPTOMS
Progression to critical temperature and multiorgan system failure may be slower than during malignant hyperthermia.
Triggered by dopamine receptor antagonists rather than inhalation anesthetics.[82][83]
INVESTIGATIONS
Absence of other causes of temperature elevation and rigidity and presence of the drug in the plasma.
Baclofen withdrawal syndrome
SIGNS / SYMPTOMS
Chronic exposure to baclofen and sudden termination of administration may be followed after several hours with severe dystonia, critical temperature, and multiorgan system failure.[61]
INVESTIGATIONS
A low plasma or cerebrospinal fluid concentration of baclofen.
Thyrotoxicosis
SIGNS / SYMPTOMS
Muscle tone is normal.
Increases in metabolism are less marked.[84]
Pseudohyperthyroidism can be induced by some weight loss dietary supplements.
INVESTIGATIONS
Blood gas to assess pCO2 and pH is normal.
Triiodothyronine (T3) is elevated.
Pheochromocytoma
SIGNS / SYMPTOMS
Headache and weight loss may be present.
Extremities may be cool.
INVESTIGATIONS
Plasma or urinary catecholamines are elevated.
PET scanning of the abdomen and/or thorax reveals the pheochromocytoma.
Drug-induced muscle injury
SIGNS / SYMPTOMS
A history of the use of known drug triggers (usually statins) is present.
Muscle pain and sometimes muscle edema precede temperature elevation.
INVESTIGATIONS
No differentiating tests.
MDMA toxicity
Use of designer drugs or psychoactive substances (e.g., alpha-PVP or flakka)
Exertional heat stroke
SIGNS / SYMPTOMS
Hyperventilation and dehydration are present.
INVESTIGATIONS
Blood gas shows a low pCO2.
Thermal dysregulation
SIGNS / SYMPTOMS
A history of recent exposure to a pyrogen is usually present.
INVESTIGATIONS
No differentiating tests.
Iatrogenic overheating
SIGNS / SYMPTOMS
Usually occurs during surgery at small, superficial surgical sites such as the ear when the rest of the patient is covered by occlusive drapes.
Administration of heat during anesthesia.
INVESTIGATIONS
No differentiating tests.
Cocaine toxicity
SIGNS / SYMPTOMS
History of drug seeking behavior, exposure to cocaine.
Mydriasis and increased psychomotor activity are present.
Symptoms improve as cocaine is metabolized.
INVESTIGATIONS
Urine cocaine assay: detection limit of >300 nanograms/mL of benzoylecgonine.
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