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Fever of unknown origin: interesting feline cases (Proceedings)

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Nov 01, 2010

Cats with fevers (103° F-106° F) are a common occurrence in everyday practice. Most cases respond to antibiotic therapy or are self-limiting (abscesses, viral infections, post-surgical fevers). However, the most frustrating case is one in which a routine course of antibiotics does not improve the clinical condition of the cat, routine diagnostics do not identify the cause and the fever is ongoing. This is the fever of unknown origin (FUO) case that requires a methodical approach to discover the exact cause of the fever so that proper therapy can be instituted. Your approach may vary based on the clinical presentation of each cat, as well as the patient's geographic location/travel history. You must also consider the cost/benefit of the diagnostic testing as well as the invasiveness of the tests performed. Tests may need to be repeated as the case progresses.

The Approach:

     • Obtain a complete history, including travel, vaccination, drug/supplements.
     • Perform a complete physical examination (repeat this step often).
     • Collect the minimum data base.
     • CBC, Biochemistry profile, Urinalysis, FeLV/FIV test
     • Thoracic and abdominal radiographs

Cause of the fever is still not defined, so the hunt continues....

     • Culture
     • Urine – aerobic and Mycoplasma, even when urine sediment is inactive. May need to culture urine repeatedly if history, clinical signs or other findings suggest urinary tractconcerns.
     • Blood – aerobic, anaerobic, Mycoplasma. Consider volume and timing of blood draws.
     • Joint – aerobic, anaerobic, Mycoplasma
     • Other (BAL fluid, feces, effusions)
     • Also consider culturing for: Mycobacteria, other atypical bacteria, fungi
     • PCR tests also available for some organisms (Mycoplasma)
     • Imaging
     • Ultrasound (Abdominal, Echocardiography, areas of swelling)
     • CT/MRI – may reduce the need for exploratory surgery

Follow any leads noted on history, physical examination or localizing signs.

     • Lameness – Joint fluid for cytology, cultures (aerobic, anaerobic, Mycoplasma), joint radiographs
     • Swellings/ lymph nodes/ effusions/ mass lesions – needle aspirate for cytology/ cultures
     • Bone marrow aspirates
     • Respiratory signs – Airway wash, lung aspirate
     • Infectious disease titers – consider specificity and sensitivity of the tests, disease prevalence, use of acute and convalescent titers
     • Immune panels – Antinuclear antibody (ANA), rheumatoid factor (RF), Coombs test
     • Tissue biopsies

While performing the hunt, don't forget to treat the patient.

     • Therapeutic drug trials – Weigh risks versus benefits.
     • Broad spectrum antibiotic therapy: Baytril or other fluoroquinolone, clindamycin
     • Unusual bacteria, rickettsial, Mycoplasma: Doxycycline
     • Fungal: Fluconazole or other antifungal
     • Immune/neoplasia: Corticosteroid therapy (prednisolone)

The fever should break within 3 days if the drug therapy is going to work for that case...

Maintain hydration – fluid therapy as needed.

Encourage appetite. Appetite will typically return once the fever breaks.