A challenging case: Getting to the source of a dog's chronic spinal pain - Veterinary Medicine
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A challenging case: Getting to the source of a dog's chronic spinal pain
After the owner's decision to discontinue treatment too soon, this dog's lumbosacral pain and subsequent lameness took a lot of time, testing, and additional treatment to get under control.


An additional complicating factor in the management of these animals is that treatment of B. canis infections is difficult and requires long-term antimicrobial therapy. Even when appropriate antimicrobial regimens and treatment durations are used, relapses of clinical signs are common.14 No treatment protocols have been shown to completely and permanently clear dogs of infection. Using a combination of dihydrostreptomycin and doxycycline, long considered the treatment of choice for canine brucellosis, is no longer possible because of the limited availability of dihydrostreptomycin.28 Dihydrostreptomycin and other aminoglycoside substitutes also require parenteral administration, which can make treatment with these agents impractical for some owners. The combination of fluoroquinolones and tetracyclines has shown promise in vitro, but clinical data supporting its efficacy are lacking.29 Appropriate antimicrobial treatment durations have not yet been adequately documented in dogs with brucellosis. Resolution of clinical signs, cessation of bacteremia, and repeatable seronegative status may be used to guide treatment, but elimination of infection is difficult to confirm antemortem. These ramifications make accurate diagnosis of the causative agent of diskospondylitis critical. Surgical intervention may be warranted in dogs with diskospondylitis that have severe neurologic signs and fail to respond to conservative treatment or when vertebral instability or spinal cord compression is present. The lesion's site, extent, and surgical accessibility must also be considered.

Serologic testing is commonly used to screen for B. canis infection, but questionable test validity and interpretation make obtaining an accurate diagnosis difficult.30 When serologic tests are used, it is important to interpret the results with knowledge of each test's sensitivity and specificity. Numerous serologic tests are available; the most commonly used tests are the 2-mercaptoethanol rapid slide agglutination test (2-ME-RSAT), 2-ME tube agglutination test (2-ME-TAT), and agarose gel immunodiffusion (AGID) test. Each of these tests has relative strengths and weaknesses. The 2-ME-RSAT and 2-ME-TAT are considered screening tests and are highly sensitive for infection. However, test results are often negative during the first five to eight weeks of infection, and both tests are troubled by cross-reactivity with antibodies to other bacterial species, often leading to false positive results.30 The 2-ME-TAT provides semiquantitative results, which can be useful in monitoring a patient's response to therapy. Two types of AGID tests are available: the AGID1 uses cell wall antigens and the AGID2 uses cytoplasmic antigens.30 The AGID1 test is highly sensitive and produces positive results in a similar time frame to that of the 2-ME-RSAT and 2-ME-TAT, but nonspecific reactions can result in false positive results.31 The AGID2 is the least sensitive of the commonly used serologic tests, and it does not routinely produce positive results until eight to 12 weeks after infection.31 However, it is highly specific for Brucella species, making it a good confirmatory test.31 An additional advantage of the AGID2 test is that the results remain positive for at least 12 months after the cessation of bacteremia (which may occur as early as six months after infection), while the agglutination and AGID1 tests may become diagnostically insignificant or give equivocal results during this period.32

This case emphasizes the importance of body fluid and tissue culturing. Although we are unaware of any other reports of B. canis being cultured simultaneously from the blood, urine, and reproductive tissues of a dog with diskospondylitis, routine cultures are of clinical value. Brucella canis can be isolated from several sites, including blood, urine, semen, vaginal discharge, gonadal tissue, intervertebral disk material, and cerebrospinal fluid.10,14,21,33,34 In several studies, blood culture results were positive in 45% to 75% of dogs with diskospondylitis, and urine culture results were positive in 25% to 60% of dogs.35-37 A report of B. canis diskospondylitis found blood culture results were positive in 30% of cases, and urine culture results were positive in 33% of cases.14

Characteristic radiographic signs of diskospondylitis include disk space collapse, bone lysis in the end plate region, end plate sclerosis, and variable bone proliferation.1,4,10 The severity and progression of radiographic lesions are highly variable and correlate poorly with clinical signs.1 It is important to radio-graph the vertebral column cranial and caudal to the lesions to accurately define the extent of vertebral involvement.


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