Approach To Fever Flashcards
Define what temperature is and what is a normal temperature?
Temperature: The hypothalamic thermoregulatory center balances excess heat production from metabolic activity in muscle and liver with heat dissipation from
the skin and lungs to maintain a normal body temperature of 36.8° ± 0.4°C with diurnal variation (lower in a.m., higher in p.m.).
Define fever
Fever: an elevation of body temperature (>37.2°C in the morning and >37.7°C in the evening) in conjunction with an increase in the hypothalamic set point.
Define fever of unknown origin
Fever of unknown origin (FUO): temperatures >38.3°C on two or more occasions and an illness duration of ≥3 weeks, with no known immunocompromised state and unrevealing laboratory and radiologic investigations into the cause
Define Hyperpyrexia
Hyperpyrexia: temperatures >41.5°C that can occur with severe infections but more commonly occur with CNS hemorrhages
Define hyperthermia
Hyperthermia: an uncontrolled increase in body temperature that exceeds the body’s ability to lose heat without a change in the hypothalamic set point. Hyperthermia does not involve pyrogenic molecules.
What is a pyrogen?
Pyrogen: any fever-causing substance, including exogenous pyrogens (e.g., micro-
bial toxins, lipopolysaccharide, superantigens) and pyrogenic cytokines (e.g., IL-1,
IL-6, TNF)
What is the pathogenesis of fever?
Pathogenesis: The hypothalamic set point increases, causing peripheral vasoconstriction (i.e., heat conservation). The pt feels cold as a result of blood shunting to the internal organs. Mechanisms of heat production (e.g., shivering, increased hepatic thermogenesis) help to raise the body temperature to the new set point. Increases in peripheral prostaglandin E2 account for the nonspecific myalgias and arthralgias that often accompany fever. When the set point is lowered again by resolution or treatment of fever, processes of heat loss (e.g., peripheral vasodilation and sweating) commence.
What are important features on history?
- chronology of events (e.g., in the case of rash: the site of onset and the direction and rate of spread)
- relation of symptoms to medications
- pet exposure
- sick contacts,
- sexual contacts
- travel
- trauma
- presence of prosthetic materials
What are the important features on physical examination?
●A consistent site for taking temperatures should be used.
●Temperature–pulse dissociations (relative bradycardia) should be noted - e.g. typhoid fever, brucellosis, leptospirosis, factitious fever
●Drug and toxin history, including antimicrobials
●Localizing symptoms
●Close attention should be paid to any rash, with precise definition of salient features.
What are the salient features of rash?
- Lesion
•Lesion type (e.g., macule, papule, nodule, vesicle, pustule, purpura, ulcer) •configuration (e.g., annular or target), •arrangement
•distribution (e.g., central or peripheral) - Classification of rash
a. Centrally distributed maculopapular eruptions (e.g., viral exanthems, exanthematous drug-induced eruptions)
b. Peripheral eruptions (e.g., Rocky Mountain spotted fever, secondary
syphilis, bacterial endocarditis)
c. Confluent desquamative erythemas (e.g., toxic shock syndrome)
d. Vesiculobullous eruptions (e.g., varicella, primary HSV infection, ecthyma gangrenosum)
e. Urticaria-like eruptions: in the presence of fever, usually due to urticarial vasculitis caused by serum sickness, connective-tissue disease, infection
(hepatitis B virus, enteroviral, or parasitic infection), or malignancy particularly lymphoma)
f. Nodular eruptions (e.g., disseminated fungal infection, erythema nodosum, Sweet’s syndrome)
g. Purpuric eruptions (e.g., meningococcemia, viral hemorrhagic fever, disseminated gonococcemia)
h. Eruptions with ulcers or eschars (e.g., rickettsial diseases, tularemia, anthrax)
What investigations should be considered?
●Complete blood count, including differential and platelet count
●ESR, and C-reactive protein
●Blood cultures (three sets drawn from different sites with an interval of at least several hours between each set; in cases in which antibiotics are indicated, all blood cultures should be obtained before administering antibiotics)
●Routine blood chemistries, including liver enzymes and bilirubin
●If liver tests are abnormal, hepatitis A, B, and C serologies
●Creatine kinase, antinuclear antibodies, rheumatoid factor
●Urinalysis, including microscopic examination, and urine culture
●Chest radiograph
●Abdominal ultrasonography
●Other tests as indicated by history and physical examination
What are common etiologies of FUO?
Infections ●Tuberculosis ●Abcesses ●Osteomyelitis ●Infective Endocarditis
Malignancies ●Lymphoma, especially non-Hodgkin's ●Leukemia ●Renal cell carcinoma ●Hepatocellular carcinoma or other tumors metastatic to the liver
Connective tissue diseases
●Vasculitis eg GCA, PAN, Takayasu, Wegener’s
●Rheumatoid arthritis
●Adult Still’s disease
Drugs
●Antimicrobials (sulfonamides, penicillins, nitrofurantoin, vancomycin, antimalarials)
●H1- and H2-blocking antihistamines
●Antiepileptic drugs (barbiturates and phenytoin)
●Iodides
●Nonsteroidal antiinflammatory drugs (including salicylates)
●Antihypertensive drugs (hydralazine, methyldopa)
●Antiarrhythmic drugs (quinidine, procainamide)
●Antithyroid drugs
●Contaminants such as quinine that accompany injected cocaine or heroin
What are the uncommon etiologies of FUO?
Factitious fever
Disordered heat homeostasis
●hypothalamic dysfunction
●abnormal heat dissipation
●excessive heat production
Dental abcess
Concurrent infection (e.g. Multiple opportunistic infections in HIV)
Other infections
●With pulmonary manifestations
Q fever, leptospirosis, psittacosis, tularemia, and melioidosis
●Without pulmonary manifestations
secondary syphilis, disseminated gonococcemia, chronic meningococcemia, visceral leishmaniasis, Whipple’s disease, and yersiniosis
Alcoholic Hepatitis
What are the basic principles of treating fever?
• The use of antipyretics is not contraindicated in common viral or bacterial infections and can relieve symptoms without slowing resolution of infection. With-holding of antipyretics may be useful, however, in evaluating the effectiveness of a particular antibiotic or in diagnosing conditions with temperature–pulse dis-
sociations or relapsing fevers (e.g., infection with Plasmodium or Borrelia species).
• Treatment of fever in pts with preexisting impairment of cardiac, pulmonary, or
CNS function is recommended to reduce oxygen demand.
• Aspirin, NSAIDs, and glucocorticoids are effective antipyretics. Acetaminophen
is preferred because it does not mask signs of inflammation, does not impair platelet function, and is not associated with Reye’s syndrome.
• Hyperpyretic pts should be treated with cooling blankets in addition to oral antipyretics
What are the basic principles of treating FUO?
- Empirical therapeutic trials with antibiotics, glucocorticoids, or antituberculous agents should be avoided in FUO except when a pt’s condition is rapidly deterio-
rating after diagnostic tests have failed to provide a definitive result. - Hemodynamic instability and neutropenia may prompt earlier empirical anti-infective therapies.
- Use of glucocorticoids and NSAIDs should be avoided unless infection and malignant lymphoma have been largely ruled out and unless inflammatory disease is both probable and debilitating or life-threatening.
- Anakinra, a recombinant form of the naturally occurring IL-1 receptor antagonist, blocks the activity of both IL-1α and IL-1β and is extremely effective in the treatment of many autoinflammatory syndromes. A therapeutic trial with anakinra can be considered in pts whose FUO has not been diagnosed after later-stage diagnostic tests
