Fever & Hyperthermia

Key Features

Essentials of Diagnosis

• Inquire about

  • Age; injection substance use

  • Localizing symptoms; weight loss, joint pain

  • Immunosuppression or neutropenia; history of cancer; risk of COVID-19

  • Medications

  • Travel

General Considerations

• Fever is a regulated rise to a new "set point" of body temperature mediated by pyrogenic cytokines

• Hyperthermia is not mediated by cytokines

  • Occurs when body metabolic heat production or environmental heat load exceeds normal heat loss capacity

  • May rise to levels capable of brain damage due to protein denaturation

• The fever pattern is of marginal value, except for the relapsing fever of malaria, borreliosis, and lymphoma (especially Hodgkin disease)

• Fever, with rash and eosinophilia, define the drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome

• Most febrile illnesses are

  • Due to common infections

  • Short lived

  • Relatively easy to diagnose

• A normal body temperature based on a peripheral thermometer (tympanic membrane, temporal artery, axillary, oral) does not always exclude the presence of a fever

• Rectal is more reliable than oral temperature, particularly in patients who

  • Breathe through their mouth

  • Are tachypneic

  • Are in an ICU setting where a rectal temperature probe can be placed

• Fever in the neurointensive care unit

  • Can occur directly from brain injury (so-called "central fever")

  • Following criteria predict "central fever" with 90% probability

    • Occurs < 72 hours after neurologic ICU admission

    • Presence of subarachnoid or intraventricular hemorrhage

    • Brain tumor

    • Absence of infiltrate on chest radiograph

    • Negative cultures

  • Serum procalcitonin and C-reactive protein (CRP) may have some utility in differentiating infectious and central fever in the ICU

Clinical Findings

Symptoms and Signs

• Fever is defined as an elevated body temperature exceeding 38.3°C

• The average normal oral body temperature taken in mid morning is 36.7°C (range 36.0–37.4°C)

• The normal rectal or vaginal temperature is 0.5°C higher; the axillary temperature is 0.5°C lower

• The normal diurnal temperature variation is 0.5–1.0°C—lowest in the early morning and highest in the evening

• There is a slight sustained temperature rise following ovulation, during the menstrual cycle, and in the first trimester of pregnancy

• Spinal cord injury may cause fever by the loss of supraspinal control of the sympathetic nervous system and defective thermoregulation due to loss of sensation

Differential Diagnosis

Common causes

• Infections

  • Bacterial

  • Viral

  • Rickettsial

  • Fungal

  • Parasitic

• Autoimmune diseases

• CNS diseases

  • Head trauma

  • Mass lesions

• Malignant disease

  • Renal cell carcinoma

  • Primary or metastatic liver cancer

  • Leukemia

  • Lymphoma

• Cardiovascular diseases

  • Myocardial infarction

  • Thrombophlebitis

  • Pulmonary emboli

• Gastrointestinal diseases

  • Inflammatory bowel disease

  • Alcoholic hepatitis

  • Granulomatous hepatitis

• Miscellaneous diseases

  • Drug fever

  • Sarcoidosis

  • Familial Mediterranean fever

  • Tissue injury

  • Hematoma

  • Factitious fever

Hyperthermia

• Hyperthermia occurs in

  • Heat stroke

  • Malignant hyperthermia of anesthesia

  • Malignant catatonia or ...