Diskospondylitis

Diskospondylitis is an inflammatory and infectious disease affecting the intervertebral disc, vertebral endplates, and adjacent vertebral bodies. It is most commonly caused by bacterial infection, with fungal etiologies less frequent. The condition typically involves the thoracolumbar and lumbosacral regions, but can affect any part of the vertebral column. It is characterized by osteomyelitis of the vertebral endplates and discitis, leading to pain, spinal instability, and potential neurological deficits. The disease can be classified based on the causative organism (bacterial vs. fungal), the location (cervical, thoracolumbar, lumbosacral), and the chronicity (acute, subacute, chronic). Systemic signs such as fever and lethargy may be present, but often the predominant clinical sign is spinal pain. If left untreated, it can progress to pathological fractures, spinal cord compression, and severe neurological dysfunction.

The most common causative agents are bacteria, with Staphylococcus pseudintermedius and Staphylococcus aureus being the most frequently isolated in dogs. Other bacteria include Streptococcus spp., Escherichia coli, Proteus spp., Pasteurella spp., Brucella canis, and anaerobic organisms. Fungal etiologies include Aspergillus spp., Paecilomyces spp., and rarely Coccidioides immitis, Blastomyces dermatitidis, and Histoplasma capsulatum. In cats, bacterial causes are similar, but fungal infections are more common than in dogs. The infection typically spreads hematogenously from a primary source such as the urinary tract, skin, oral cavity, or endocarditis. Direct extension from a penetrating wound or surgical contamination is less common. In some cases, the causative organism cannot be identified despite extensive testing.

Diskospondylitis is most commonly diagnosed in dogs, with a higher incidence in large and giant breeds such as German Shepherds, Labrador Retrievers, and Great Danes. There is no strong sex predilection, though some studies suggest a slight male predominance. The disease can occur at any age, but middle-aged dogs (4-7 years) are more commonly affected. Cats are less frequently affected, but when they are, fungal infections are more likely. Geographic variation exists, with fungal causes more prevalent in certain regions (e.g., Aspergillus in German Shepherds in the southeastern United States). No clear seasonal pattern is reported, but some studies suggest a higher incidence in warmer months, possibly due to increased outdoor activity and exposure to pathogens.

The pathophysiology of diskospondylitis begins with hematogenous seeding of bacteria or fungi into the vertebral endplate, which has a rich blood supply. The organisms adhere to the subchondral bone, causing osteomyelitis. The infection then spreads to the intervertebral disc, leading to discitis and subsequent destruction of the disc and adjacent vertebral bodies. The inflammatory response includes infiltration of neutrophils and macrophages, leading to tissue necrosis and bone lysis. As the infection progresses, the vertebral bodies may collapse, resulting in spinal instability and potential spinal cord compression. In chronic cases, new bone formation (spondylosis) may occur as a reparative response. The release of inflammatory mediators and cytokines contributes to pain and systemic signs. Neurological deficits arise from direct compression, ischemia, or pathological fracture.

Predisposing factors include immunosuppression (e.g., from corticosteroid therapy, concurrent diseases such as diabetes mellitus or hyperadrenocorticism), urinary tract infections (which serve as a source of bacteremia), skin infections, dental disease, and endocarditis. Large breed dogs with a genetic predisposition to fungal infections (e.g., German Shepherds with aspergillosis) are at higher risk. Trauma or previous spinal surgery may also predispose to local infection. Poor dental hygiene and periodontal disease are significant risk factors due to the high incidence of bacteremia. In addition, any condition that compromises the immune system increases susceptibility to hematogenous spread.

The most common clinical sign is spinal pain, which may be localized to the affected region. Pain can be severe and may be elicited on palpation or movement. Neurological deficits vary depending on the location and severity of the lesion. In thoracolumbar disease, signs may include ataxia, paresis, and proprioceptive deficits. Cervical lesions may cause neck pain, stiffness, and tetra- or hemiparesis. Lumbosacral involvement can lead to pelvic limb weakness, lameness, and cauda equina syndrome. Systemic signs such as fever, lethargy, anorexia, and weight loss may be present, especially in acute cases. In chronic cases, muscle atrophy and kyphosis may be observed. Some animals may have a history of recurrent urinary tract infections or other primary infections.

Differential diagnoses include: 1) Intervertebral disc disease (IVDD) - typically acute onset, with no systemic signs, and imaging shows disc extrusion or protrusion without vertebral endplate lysis. 2) Spinal neoplasia (e.g., osteosarcoma, multiple myeloma) - may show lytic bone lesions but usually lacks disc involvement and systemic signs; biopsy is definitive. 3) Spondylosis deformans - non-inflammatory, degenerative condition with ventral vertebral osteophytes, no pain or neurological deficits typically. 4) Vertebral fracture or luxation - history of trauma, imaging shows fracture lines without disc lysis. 5) Meningomyelitis - inflammation of the meninges and spinal cord, often with CSF pleocytosis, but no vertebral changes. 6) Discospondylitis due to fungal infection - similar clinical signs, but imaging may show more extensive bone lysis and periosteal reaction; serology or culture for fungi is needed. 7) Epidural abscess - may cause similar signs but is usually associated with a focal mass effect; MRI is helpful. 8) Spinal lymphoma - can cause vertebral lysis but typically involves multiple sites and has characteristic cytology.

The diagnostic approach begins with a thorough history and physical examination, including a complete neurological examination to localize the lesion. Baseline blood work (CBC, serum biochemistry, urinalysis) is recommended to identify systemic inflammation and concurrent infections. Blood cultures are indicated in febrile patients or those with suspected bacteremia. Urine culture is essential as urinary tract infections are a common source. Imaging is the cornerstone of diagnosis: survey radiography of the spine may show characteristic changes such as narrowing of the intervertebral disc space, lysis of the vertebral endplates, and new bone formation. However, radiographs may be normal in early cases. Advanced imaging (CT or MRI) is more sensitive and is recommended if radiographs are inconclusive or if surgical intervention is planned. MRI is particularly useful for assessing spinal cord compression and soft tissue involvement. If a causative organism is not identified, fluoroscopic-guided fine-needle aspiration or biopsy of the affected disc/vertebral body can be performed for cytology and culture. Serology for Brucella canis is recommended in endemic areas or in intact dogs. CSF analysis may be performed to rule out meningitis, but it is often normal in diskospondylitis.

Complete blood count may reveal leukocytosis with a left shift, though in chronic cases it may be normal. Serum biochemistry may show mild hyperglobulinemia and hypoalbuminemia due to chronic inflammation. Urinalysis may reveal evidence of urinary tract infection (pyuria, bacteriuria, hematuria). Blood cultures are positive in approximately 30-50% of cases. Urine culture is positive in up to 50% of cases. Serology for Brucella canis (rapid slide agglutination test or agar gel immunodiffusion) is recommended. In fungal cases, serology for Aspergillus (galactomannan assay) or other fungal antigens may be helpful. C-reactive protein (CRP) may be elevated as an acute-phase protein. In cases with neurological deficits, cerebrospinal fluid analysis may show mild pleocytosis and elevated protein, but it is not specific.

Radiography: Findings include narrowing of the intervertebral disc space, irregularity and lysis of the vertebral endplates, and sclerosis of adjacent bone. In chronic cases, ventral spondylosis and vertebral body collapse may be seen. Radiographs are most sensitive in the thoracolumbar region, but early lesions may be missed. Ultrasonography: Not typically used for spinal imaging, but may be used to evaluate the urinary tract for infection. Computed Tomography (CT): Provides detailed bone assessment, showing endplate lysis, disc space narrowing, and new bone formation. CT is more sensitive than radiography and can guide needle aspiration. Magnetic Resonance Imaging (MRI): The most sensitive modality, showing increased signal intensity on T2-weighted images in the disc and vertebral bodies, and contrast enhancement on T1-weighted images. MRI is excellent for assessing spinal cord compression and soft tissue extension. Nuclear scintigraphy (bone scan) can detect early increased uptake but is less specific.

Fine-needle aspiration of the affected disc or vertebral body can be performed under fluoroscopic or CT guidance. Cytology may reveal inflammatory cells (neutrophils, macrophages) and, if stained appropriately, may show bacteria or fungal organisms. Histopathology of biopsy samples shows osteomyelitis with necrosis, fibrosis, and inflammatory infiltrate. Special stains (Gram stain, silver stain for fungi) can help identify the organism. Culture of the aspirate or biopsy is essential for definitive diagnosis and antimicrobial susceptibility testing.

Treatment typically involves prolonged antimicrobial therapy (4-8 weeks or longer) based on culture and sensitivity results. If no organism is identified, empirical therapy with a broad-spectrum antibiotic such as amoxicillin-clavulanate (12.5-25 mg/kg PO q8h) or a first-generation cephalosporin (e.g., cefazolin 22 mg/kg IV q8h) is initiated. For methicillin-resistant infections, alternatives include clindamycin (11 mg/kg PO q12h) or enrofloxacin (5-10 mg/kg PO q24h). In cases of fungal infection, antifungal agents such as fluconazole (5-10 mg/kg PO q12h) or itraconazole (5-10 mg/kg PO q24h) are used. Pain management is crucial: NSAIDs (e.g., carprofen 2.2 mg/kg PO q12h) or opioids (e.g., tramadol 2-5 mg/kg PO q8h) are commonly used. Strict rest and confinement are recommended to prevent pathological fractures. In cases with severe pain, neurological deficits, or spinal instability, surgical debridement and stabilization may be necessary. Supportive care includes fluid therapy, nutritional support, and physical rehabilitation.

The prognosis for diskospondylitis is generally good with early diagnosis and appropriate treatment. Most animals show significant improvement within 1-2 weeks of therapy. The overall recovery rate is reported to be 70-90%. Negative prognostic factors include severe neurological deficits, fungal etiology, delayed treatment, and the presence of pathological fractures. Recurrence is possible if the primary source of infection is not controlled or if antimicrobial therapy is discontinued prematurely. Long-term follow-up is essential to monitor for resolution and to adjust therapy as needed.

Recheck examinations should be performed every 2-4 weeks during the initial treatment phase. Serial radiographs or advanced imaging (CT/MRI) may be repeated at 4-8 weeks to assess healing. Blood work (CBC, biochemistry) and urine cultures should be repeated to ensure resolution of infection. Antimicrobial therapy should be continued for at least 4-8 weeks after clinical resolution, and some cases require 3-6 months of therapy. In cases of fungal infection, treatment may be prolonged for 6-12 months. Regular monitoring for adverse effects of long-term antimicrobial or antifungal therapy is important. Owners should be advised to restrict activity during the recovery period and to gradually resume normal exercise.

Pearls: 1) Always obtain urine culture and blood cultures in suspected cases, as they often identify the causative organism. 2) MRI is the most sensitive imaging modality for early detection. 3) Consider fungal causes in immunocompromised or large breed dogs, especially German Shepherds. 4) Prolonged antimicrobial therapy is essential; do not stop early. 5) Pain management is critical for patient comfort and to facilitate recovery. Pitfalls: 1) Relying solely on radiographs may miss early lesions. 2) Failing to perform culture and sensitivity can lead to inappropriate antibiotic selection. 3) Underestimating the risk of pathological fractures, especially in large breed dogs. 4) Not considering concurrent infections (e.g., endocarditis) that may require additional treatment. 5) Discontinuing antibiotics prematurely can lead to recurrence.

Antimicrobials: Amoxicillin-clavulanate (12.5-25 mg/kg PO q8h) is a first-line choice. Cefazolin (22 mg/kg IV q8h) for initial hospitalization. Clindamycin (11 mg/kg PO q12h) is effective against anaerobic and gram-positive bacteria. Enrofloxacin (5-10 mg/kg PO q24h) for gram-negative infections. For methicillin-resistant Staphylococcus, consider vancomycin (15 mg/kg IV q8h) or linezolid (10 mg/kg PO q12h) based on susceptibility. Antifungals: Fluconazole (5-10 mg/kg PO q12h) for systemic fungal infections. Itraconazole (5-10 mg/kg PO q24h) for aspergillosis. Analgesics: Carprofen (2.2 mg/kg PO q12h) or meloxicam (0.1 mg/kg PO q24h) for pain and inflammation. Opioids such as tramadol (2-5 mg/kg PO q8h) or fentanyl patches (2-5 mcg/kg/hr) for severe pain. Muscle relaxants like methocarbamol (15-20 mg/kg PO q8h) may be used for muscle spasms. All dosages should be adjusted based on renal and hepatic function. Avoid NSAIDs in patients with renal impairment or gastrointestinal disease.

Several studies have evaluated the clinical features and treatment outcomes of diskospondylitis in dogs. A retrospective study by Burkert et al. (2005) reported that Staphylococcus was the most common isolate, and that MRI was superior to radiography for diagnosis. Another study by Ruoff et al. (2017) found that prolonged antibiotic therapy (median 8 weeks) resulted in a 90% success rate. Consensus guidelines from the ACVIM (2015) on infectious diseases recommend blood and urine cultures before initiating antibiotics, and advanced imaging (CT/MRI) for suspected cases. A study by Tipold et al. (2016) highlighted the importance of considering fungal causes in German Shepherds. Overall, the literature supports early aggressive therapy with appropriate antimicrobials and pain management, with a good prognosis in most cases.