fever

Introduction

Fever is an abnormal elevation of body temperature due to a change in the hypothalamic thermoregulatory center located in the anterior hypothalamus. This change is largely mediated by release of endogenous pyrogen(s) by circulating monocytes & tissue macrophages (IL-6 may be the most important endogenous pyrogen). This in turn results in production of hypothalamic prostaglandins, especially PGE2. Heat production & heat loss are thus balanced to maintain a higher body temperature. The definition of fever is arbitrary; some definitions are:

• a core temperature > 38.0 C (100.4 F)
• 2 consecutive temperatures > 38.3 C (101 F)

- 38.1 C

(Also see fever in the elderly)

Hyperthermia without fever may result from failure to adequately dissipate body heat (e.g., a hot environment), or drugs (e.g., malignant hyperthermia). True fever may arise from numerous sources including infection, inflammation, infarction or trauma, neoplasms, or metabolic disorders.

Etiology

(some causes may not represent true fever)

• infection
  • bacterial
  • viral
  • parasitic
  • fungal
• immunologic disorders associated with inflammation
  • connective tissue disease
  • *acute arthritis
  • vasculitis
  • serum sickness
  • immune hemolytic anemia
• neoplasm
  • common with reticuloendothelial tumors
  • less commonly with solid tumors
• thrombophlebitis
  • deep vein thrombosis
  • pulmonary embolus
• infarction
  • myocardial infarction
  • stroke
• trauma: crush injury to muscle
• *pharmacologic agents
• other causes
  • acute attack of gout
  • acute porphyria
  • acute adrenal insufficiency
  • hyperthyroidism
  • pheochromocytoma
  • tonic clonic seizures

Pathology

• endogenous pyrogens
  • interleukin-1 (IL-1)
  • tumor necrosis factor (TNF) - alpha
  • interleukin-6 (IL-6)
• organum vasculosum lamina terminalis with its fenestrated endothelium provides contact of peripheral blood through blood brain barrier to preoptic & anterior hypothalamus
• PGE2 within the hypothalamus initiates fever

History

• onset, pattern, cough, sputum, sore throat, headache, neck stiffness, dysuria, frequency, night sweats, vaginal discharge, back pain, myalgia, nausea/vomiting, diarrhea, chest pain, abdominal pain, ear pain, arthralgias, bone pain, recent antipyretic use, diabetes, valvular heart disease, recent surgery, HIV risk factors, travel, exposure to tuberculosis, hepatitis, animals, ill contacts, recent antibiotic use

Clinical manifestations

(associated signs/symptoms)

• altered mental status
  • lethargy
  • confusion
  • stupor
  • coma
• ears, nose & throat
  • earache, inflamed tympanic membranes
  • sore throat, pharyngeal erythema &/or exudate
  • sinus tenderness
  • nasal exudate or nasal congestion
• neck: cervical lymphadenopathy
• lungs
  • rales or rhonchi
  • evidence of consolidation or effusion
  • cough
  • sputum
• heart: murmur of regurgitation
• abdomen
  • rebound tenderness
  • focal tenderness
  • guarding
• genitourinary
  • costovertebral angle (CVA) tenderness
  • cervical motion tenderness
  • cervical exudate
  • adnexal tenderness
  • dysuria
  • frequency
  • urgency
• rectal tenderness, swelling or exudate
• extremities
  • focal erythema, swelling or tenderness
  • joint effusion, especially monoarticular
• skin
  • petechiae
  • pustules
  • rash

Laboratory

• specific tests based upon clinical syndrome
• febrile adults without localizing symptoms, neutropenic or immunocompromised patients
  • complete blood count (CBC)
    • WBC > 15,000/mm3 (14,000 in elderly)
    • neutrophils < 1000/mm3
    • bands > 1500/mm3 (> 6% in elderly)
  • sputum evaluation
    • gram stain, acid fast-stain, fungal stain
    • culture
  • urinalysis & culture
    • pyuria of > 5 WBC/hpf suggests urinary tract infection
    • absence of pyuria excludes diagnosis except in neutropenic patients
    • especially well-appearing children < 2 years of age
  • blood cultures: most useful when WBC &/or neutrophil/band count is abnormal
  • serum chemistries
    • chem-7 (electrolytes, serum urea nitrogen, serum creatinine, serum glucose)
    • liver function tests
    • serum creatine-kinase
  • cerebrospinal fluid examination
  • evaluation of any abnormal fluid collections
    • pleural fluid
    • peritoneal fluid
    • joint fluid
    • abscesses

Radiology

• chest X-ray: clinical exam less useful than chest X-ray in detecting pulmonary consolidation

Management

• specific measures when specific etiology is suggested by clinical findings
• empiric antibiotic therapy when potentially serious or fatal bacterial infection is suggested by clinical findings (see empiric antibiotic therapy)
• febrile individuals with serious comorbid conditions or immunodeficiency should be treated as in B
• antipyretic therapy:
  • comfort measure
  • acetaminophen 650 mg PO/PR every 6 hours
  • ibuprofen 600-800 mg PO every 6 hours
  • ibuprofen 10 mg/kg better than acetaminophen for reducing fever in children (safety comparable)
  • alternating ibuprofen with acetaminophen may be better than monotherapy for reducing fever in children
  • ibuprofen alone as good as acetaminophen + ibuprofen

More general terms

• hyperthermia (pyrexia)

More specific terms

• drug-induced fever
• fever & rash
• fever in a returning traveler
• fever in the elderly
• fever of unknown origin (FUO)
• pharyngoconjunctional fever (PCF)
• postoperative fever
• quotidian fever
• recurrent fever
• relapsing fever
• saddle-back fever
• tick fever

Additional terms

• chills/rigors
• pyrogen
• temperature