Types of Fever

Rigor is a fever characterized by a sudden shivering attack in which body temperature rapidly increases to hyperpyrexia levels. Unlike other fever types, rigor involves an abrupt onset of severe chills accompanying the temperature rise. This distinct presentation helps clinicians differentiate rigor from gradual fever increases caused by infection or other conditions.

Hyperthermia occurs when the thermoregulatory mechanism exhausts and fails to compensate for extra heat produced by the body, causing temperature to exceed 104°F. The body's natural cooling systems become overwhelmed by intense heat exposure or excessive internal heat generation. This differs from fever, where the body's temperature set point is elevated but regulatory mechanisms still function.

Malignant hyperthermia is a hypermetabolic response associated with uncontrolled heat generation that develops when certain anesthetic medications are administered to susceptible individuals. This genetic disorder causes a dangerous spike in body temperature during anesthesia exposure. Early recognition and immediate discontinuation of triggering anesthetics are critical for patient survival.

Heatstroke occurs due to prolonged sun exposure, resulting in body temperature rising to 104°F or higher. It is characterized by dry skin and central nervous system abnormalities including convulsions, delirium, or coma. These severe neurological symptoms distinguish heatstroke as a medical emergency requiring immediate intervention.

Neurogenic fever occurs when conditions like cerebral trauma, intracranial hemorrhage, or elevated intracranial pressure damage the hypothalamus. Because the hypothalamus controls temperature regulation, damage to this area disrupts normal thermoregulation. This type of fever does not respond to antipyretic drugs because the problem is structural damage rather than an infection-triggered temperature set point change.

Fever of unknown origin is a fever that persists for more than three weeks and remains undiagnosed even after investigations. It is typically defined as a temperature of 101°F or higher sustained over this extended period. This classification helps clinicians identify cases requiring more aggressive diagnostic workup and specialist consultation.

Fever can be caused by infection, impaired nervous system function, malignant neoplasms, blood diseases, heatstroke, dehydration, surgical trauma, crushing injuries, and allergic reactions. Understanding these diverse etiologies helps clinicians determine appropriate diagnostic approaches and treatments. Each cause category may present with distinct fever patterns and associated clinical findings.