Page 1453 - Small Animal Internal Medicine, 6th Edition

CHAPTER 90 Fever of Undetermined Origin 1425

BOX 90.1 Mountain spotted fever, bartonellosis, leishmaniasis, leuke-
mia, systemic mycoses) may cause fever. Enlarged lymph
VetBooks.ir Diagnostic Evaluation of Dog or Cat With Fever of nodes or spleen should be evaluated cytologically by per-
forming fine-needle aspiration (FNA). An FNA sample can
Undetermined Origin
First Stage also be obtained for bacterial and fungal culture and sus-
ceptibility or for PCR assay if the cytologic studies reveal
• CBC evidence of infection or inflammation. Any palpable mass or
• Serum biochemistry profile and thyroxine concentration swelling should also be evaluated by using specimens obtained
• Urinalysis by FNA to rule out granulomatous, pyogranulomatous, sup-
• Urine bacterial culture and susceptibility purative inflammation, and neoplasia (see Chapter 74).
• FNA of enlarged organs, masses, or swellings
The clinician should thoroughly inspect and palpate the
Second Stage oropharynx, searching for signs of pharyngitis, stomatitis, or
• Thoracic radiographs tooth root abscesses. The bones should also be thoroughly
• Abdominal ultrasonography palpated, particularly in young dogs, because metabolic
• Echocardiography bone disorders such as hypertrophic osteodystrophy and
• Serial bacterial blood cultures panosteitis can cause fever associated with bone pain. Palpa-
• Immune tests (antinuclear antibody, rheumatoid factor) tion and passive motion of all joints is also indicated in
• Acute-phase reactant measurements (e.g., CRP) search of monoarthritis, oligoarthritis, or polyarthritis. A
• Serum protein electrophoresis neurologic examination should be conducted to detect signs
• Serologic tests or PCR assay (see Table 90.1) of meningitis or other central nervous system lesions. In
• Arthrocentesis (cytologic studies and culture) older cats, the ventral cervical region should be palpated to
• Biopsy of any lesion or enlarged organ detect thyroid enlargement or nodules.
• Bone marrow aspiration (for cytologic studies and
bacterial and fungal culture) The thorax should be auscultated carefully in search of
• Cerebrospinal fluid analysis a murmur, which could indicate bacterial endocarditis. A
• Leukocyte or ciprofloxacin scanning thorough ocular examination may reveal changes suggestive
• Exploratory celiotomy of a specific cause (e.g., chorioretinitis in cats with feline
infectious peritonitis or in dogs with monocytic ehrlichiosis).
Third Stage
• Therapeutic trial (antipyretics, antibiotics, Clinicopathologic Evaluation
corticosteroids) A minimum database consisting of a CBC, serum biochem-
istry profile, urinalysis, urine bacterial culture, and suscep-
CBC, Complete blood count; CRP, C-reactive protein; FNA, tibility testing should always be carried out in dogs and cats
fine-needle aspiration; PCR, polymerase chain reaction.
with persistent fever. The CBC may provide important clues
regarding the cause of the fever (Table 90.2). A serum bio-
clinic (Box 90.1). The first stage consists of a thorough chemistry profile may also yield diagnostic information in
history taking and physical examination, as well as a minimal dogs and cats with FUO and can provide indirect infor-
database (CBC, serum biochemistry, urinalysis). The second mation on parenchymal organ function. Some laborato-
stage consists of additional noninvasive and invasive diag- ries include C-reactive protein (CRP) in their profile; the
nostic tests. The third stage consists of a therapeutic trial, CRP concentration is often elevated in patients with infec-
which is instituted if no diagnosis can be determined after tious and other inflammatory diseases but is not specific.
completion of the second stage. Hyperglobulinemia and hypoalbuminemia may indicate an
infectious, immune-mediated, or neoplastic disorder (see
History and Physical Examination Chapter 89). The finding of pyuria or white blood cell casts
When a febrile patient does not respond to antibacterial in a urinalysis may indicate a urinary tract infection, which
treatment, a course of action must be formulated. A thor- may be the cause of the FUO (i.e., pyelonephritis). Protein-
ough history should be obtained and a complete physical uria associated with inactive urine sediment should prompt
examination performed. The history rarely provides clues the clinician to evaluate a urine protein-to-creatinine ratio
to the cause of the fever. However, a history of ticks may to rule out glomerulonephritis or amyloidosis as the cause
indicate a vector-borne disease, administration of tetracy- of the fever.
cline (mainly to cats) may indicate a drug-induced fever, Other diagnostic tests that may be required in patients
and travel to areas in which systemic mycoses are endemic with FUO are listed in Box 90.1. Echocardiography is indi-
should prompt further investigation, consisting of cytologic cated only if the patient has a heart murmur because it rarely
or serologic studies or fungal cultures/polymerase chain detects a valvular lesion in dogs without murmurs. Some of
reaction (PCR). the infectious diseases listed in Table 90.1 can be diagnosed
During a physical examination, the lymphoreticular organs on the basis of serologic findings, culture, or PCR testing.
should be evaluated because numerous infectious diseases Fluid from several joints should be aspirated for cyto-
affecting these organs (e.g., ehrlichiosis, anaplasmosis, Rocky logic evaluation and possibly bacterial culture because