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○ Brucella canis screening test, if appropriate Chronic Treatment time to confirm that resolution of the fever can
○ Polymerase chain reaction (PCR) testing Antibiotic trials: be attributed to selected therapy.
VetBooks.ir ○ Immune tests: antinuclear antibody test initiated after all culture specimens have PROGNOSIS & OUTCOME Diseases and Disorders
for specific infectious agents
• Broad-spectrum antibiotic therapy may be
if systemic lupus erythematosus is sus-
been collected. Therapy should be based
pected; Coombs’ test if immune-mediated
hemolytic anemia is suspected but cannot on the agents most likely present, their Depends on specific cause
known antibiotic sensitivity, and the organ
be confirmed otherwise; serum protein or system affected. PEARLS & CONSIDERATIONS
electrophoresis if hyperglobulinemic • If no response is seen after 72 hours, an
• Imaging antibiotic with a different spectrum of activ- Comments
○ Abdominal ultrasound: examine for ity may be chosen; however, the clinician • Infectious disease, immune-mediated condi-
evidence of pyelonephritis, prostatitis, should first re-evaluate whether bacterial tions, and neoplasia account for > 75% of
or pyometra; identify ± aspirate enlarged infection is the underlying cause. FUO cases.
abdominal organs or masses. • Commonly used empirical antibiotics include • With comprehensive diagnostic testing,
○ Echocardiogram: identify vegetative amoxicillin-clavulanate 10-20 mg/kg PO q usually only 10% of FUO cases are con-
valvular lesions of endocarditis. 8-12h and enrofloxacin 5-10 mg/kg (dog), sidered idiopathic.
○ Spinal long bone and joint radiographs: 5 mg/kg (cat) PO q 24h; if anaerobic infec- • Immune-mediated polyarthritis will fre-
examine for evidence of discospondylitis, tion is suspected, metronidazole 10-15 mg/ quently not be associated with detectable
osteomyelitis, periosteal proliferation, kg PO q 12h or clindamycin 5-15 mg/kg PO joint swelling. Arthrocentesis is indicated in
erosive arthritis, hypertrophic osteodys- q 8-12h; if tick-borne disease is suspected, all FUO cases where no underlying cause
trophy, panosteitis. doxycycline 10 mg/kg PO q 24h or 5 mg/ has been identified, even absent a history
○ CT/MRI (p. 1132) kg PO q 12h. of lameness.
• Diagnostic procedures Antifungal trials: • Lymphoma, leukemia, myeloma, and hepatic
○ Arthrocentesis (p. 1059): polyarthritis • In areas where systemic mycoses are endemic, neoplasia are particularly common causes of
○ Bone marrow aspirates and/or biopsy antifungal agents may be used in patients fever in association with cancer.
(p. 1064): if CBC changes suggest bone with typical signs of fungal infection. • Drug fevers may occur at any time after
marrow involvement • The response to antifungal therapy may take initiation of drug therapy, even after weeks
○ CSF tap (p. 1080): if neurologic signs (± days to weeks. or months. Careful drug history is warranted,
fundic exam) suggest meningoencephalitis • Examples: itraconazole 5-10 mg/kg PO q 24h as is a trial discontinuation of drugs.
or meningitis or 5 mg/kg PO q 12h; fluconazole 5-15 mg/
○ Muscle biopsy: hepatozoonosis kg PO q 12-24h Prevention
○ Abdominocentesis (p. 1056): peritonitis Glucocorticoid trials: • Ectoparasite prevention may reduce risk of
and pancreatitis • Used when immune-mediated disease is vector-borne disease transmission.
○ Transtracheal wash or bronchoal- suspected • Indoor pets are less likely to be exposed to
veolar lavage: if respiratory involvement • Should be used only after infectious disease vector-borne diseases.
(p. 1073) has been reasonably ruled out • Vaccination against specific disease agents
○ Laparoscopy, thoracoscopy, or exploratory • A dramatic response (fever reduction, striking for at-risk pets
surgery for biopsies, as appropriate improvement in systemic signs) should be • Yearly retroviral testing ± vaccination in
seen in 24-48 hours, but glucocorticoids can high-risk cats
TREATMENT reduce fever initially even when they do not • Routine screening of geriatric pets to facilitate
effectively treat the underlying disease (e.g., early diagnosis and treatment of cancer
Treatment Overview infectious disease).
• The goal in all cases of FUO is to • Examples: prednis(ol)one 1 mg/kg PO q Technician Tips
obtain a specific diagnosis and treat 12h or dexamethasone 0.2 mg/kg IV q 24h; • Fever may wax and wane in a patient with
accordingly. dosages for long-term use are adjusted based FUO.
• A therapeutic trial should be initiated on the specific underlying cause. • Patients receiving a glucocorticoid trial should
only when a specific diagnosis cannot be be closely monitored because of the risk of
ascertained. Drug Interactions exacerbating an infectious disease.
Avoid the use of NSAIDs in combination with • It is important that owners understand that
Acute General Treatment glucocorticoids. not all fevers are due to infection and not all
• Intravenous crystalloid fluid therapy at 1.5-2 infections respond to antibiotic treatment.
times maintenance for fevers > 103.5°F Possible Complications
(>39.7°C) • Drug therapy trials without a definitive Client Education
• Mechanical cooling methods such as cool diagnosis may interfere with future diagnosis • Animals may serve as sentinels for infections
water baths or fans for fevers > 106°F (e.g., antibiotic use may impair culture) or transmit some infections to humans.
(>41.1°C) and exacerbate an undiagnosed condition • Investigation of FUO can be time consuming
• Antipyretic agents (e.g., nonsteroidal anti- that may become life-threatening (e.g., and costly.
inflammatory drugs [NSAIDs] given only glucocorticoids may worsen fungal infection).
when the patient is fully hydrated) may be • Glucocorticoids may lead to immunosup- SUGGESTED READING
considered for fevers > 106°F (>41.1°C) that pression or may mask clinical signs due to Lunn KF: Fever of unknown origin: a systematic
do not respond to fluids and cooling. their antiinflammatory effects. approach to diagnosis. Compend Contin Educ Vet
○ Antipyretics can mask the effects of other 23:976-992, 2001.
therapies and can be associated with Recommended Monitoring
adverse effects such as gastrointestinal Monitor temperature at least q 8h. Response to AUTHOR: Karen M. Tefft, DVM, MVSc, DACVIM
EDITOR: Leah A. Cohn, DVM, PhD, DACVIM
ulceration and hepatic and/or renal trial therapy may be nonspecific or coincidental,
toxicosis. and monitoring should continue for a sufficient

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