Specialty Spotlight: Diskospondylitis – Signs, Diagnosis, and Treatments
Diskospondylitis – Signs, Diagnosis, and Treatments
Christina Scanlon Isack, DVM, DACVIM (Neurology)
Discospondylitis is an infection involving the intervertebral discs and surrounding vertebral endplates. This infection is most commonly secondary to bacteria, but we occasionally see fungal discospondylitis as well. Infection is generally thought to occur secondary to:
- Hematogenous spread (most common) with involvement of the urinary tract in many cases
- Foreign body migration, such as plant awns
- Iatrogenic infection following spinal surgery or a paravertebral injection (least common)
Signalment is most commonly adult to middle-aged, large breed dogs. Purebred dogs may also be overrepresented. Males are more common than females. The most common sites of infection are the thoracolumbar and lumbosacral spine. The lumbosacral junction is the most common site. However, the cervical spine can also be affected. More than 40% of dogs will have multiple discospondylitis lesions. The presenting complaint is often severe pain, which, in some cases, can be challenging to localize initially. In the early stages of the disease, there are often minimal to no neurologic deficits associated with focal or diffuse spinal pain, fever (about 30% of cases), depression, reluctance to move, and reduced appetite.
Radiographs and/or a spinal CT scan can often reveal discospondylitis (as long as more than 7-10 days post presentation of signs). Radiographs can lag at least 7-10 days behind clinical symptoms (although reported by as much as 2-4 weeks) as there needs to be about 70% destruction of the bones of the vertebral endplates directly adjacent to the infected disc to be visible as lytic changes noted on spinal radiographs. The disc space can often be described as widened with loss of the crisp/sharp outline of the vertebral endplate and concurrent bony proliferation and endplate sclerosis. Full spine CT or survey spinal radiographs can be used to screen for other sites of discospondylitis as well as for monitoring purposes with long-term therapy.
MRI is the gold standard for definitive diagnosis. A cerebrospinal fluid analysis is generally not helpful because even if disease is severe enough to allow formation of an epidural empyema, the spinal fluid remains untouched.
If discospondylitis is found, blood and urine cultures are often recommended, as long as no antibiotic therapy has yet been initiated. Often, these cultures are negative; however, a positive culture can be very helpful to guide treatment. A positive culture is reported between 30-80% of the time; however, this is not what we really see clinically (closer to 20%). More often than not, the cultures are negative.
While any patient showing evidence of discospondylitis should be screened, dogs that are intact and/or previously used for breeding allow for public health responsibility to test for brucellosis.
German Shepherd dogs are predisposed to disseminated aspergillosis due to a deficiency in IgA antibodies. Therefore, a GSD with discospondylitis lesions should be screened with a galactomannan antigen EIA (Mira Vista Labs – 90% sensitive and specific for systemic aspergillosis). Occasionally, other lesions will occur, including uveitis and/or granulomas of the spleen, lymph nodes, and kidneys.
Fluoroscopically guided needle or surgical aspirates – possibly more sensitive than blood/urine cultures but less routinely performed as it is slightly more technically challenging.
Ideally, treatment is led by culture results. In the case of a negative culture, treatment often involves an antibiotic that has good bone penetration and covers our most commonly seen bacteria, such as Staphylococcus sp (most common) or Streptococcus sp. One of the more common antibiotics of choice is a first-generation cephalosporins. However, other penicillin-type drugs are often effective as well. If the patient has severe neurologic deficits, 5-7 days of IV antibiotics should be considered.
Ultimately, discospondylitis is treated on minimum for 6-8 months; however, some patients require longer-term or even lifelong management if symptoms keep returning. Serial spinal radiographs or CT can be used to track new/progressive lesions. If lesions are static/chronic to improved by 6-8 months, some patients are able to get off medication.
Some clinicians will also screen a C-Reactive protein (inflammatory marker) as a way to help solidify the suspicion of discospondylitis (although it is a non-specific inflammatory marker) and track progress. An elevated CRP is more consistent than things like a fever or leukocytosis in the face of discospondylitis. A return to normal CRP is desired before discontinuation of medication.
-Christina Scanlon, DVM, DACVIM (Neurology)