Clinical history
An 8-week-old female weaned domestic pig with a body weight of 20 kg at acquisition was presented to the Division of Clinical Neurology, Vetsuisse Faculty of Bern, Switzerland, due to a non-ambulatory tetraparesis. Unfortunately, little was known about the history other than the weaner was found in lateral recumbency in the box on the day before presentation without prior clinical signs being noted. The pig was weaned after 4 weeks and was held in a group of 25 weaners. It was the only weaner affected within the herd.
Clinical findings and investigation
Vital parameters revealed a rectal temperature in the lower reference range (39 °C; reference: 39.3 °C ± 0.30 °C), a moderate tachycardia (169 beats/min; reference: 90–100 beats/min), and a moderate tachypnea (60 breaths/minute; reference: 25–40/min) [18]. Other clinical findings were a stripe-formed bleeding in the subcutis of 20 cm in length and approximately 1 cm in width from the left elbow to the middle of the left scapula. Other skin lesions were detected dorsal to the left eye and in the dorsal midline of the cervical area. The tail was intact. The skin turgor was mildly reduced and the BCS was 3/5 (normal) [18].
The weaner was presented in lateral recumbency with a non-ambulatory tetraparesis. As the handling of the weaner caused significant stress in the animal, the neurological examination was abbreviated. The swine revealed a normal mental state and very stressed behavior. Proprioception seemed absent in all four limbs. Cranial nerve function was normal. The extensor tone was reduced in both thoracic and increased in both pelvic limbs (Fig. 1) and the spinal reflexes were reduced in both thoracic and normal in both pelvic limbs. The weaner seemed to be severely hyperesthetic when the caudal cervical vertebral column was palpated.
The neurological signs were consistent with a lesion localized at C6-T2 spinal cord segments [4]. Differential diagnoses comprised traumatic (i. e. vertebral fracture), inflammatory (i. e. diskospondylitis, vertebral osteomyelitis, meningomyelitis), degenerative (i. e. intervertebral disk extrusion) and vascular (i. e. spinal hematoma) etiologies.
The complete blood count showed a mild leukocytosis (22.75 × 109/L; reference: 7.9–18.5 × 109/L) without left-shift, a slight lymphopenia (4.78 × 109/L; reference: 4.9–12.1 × 109/L) and monocytosis (1.48 × 109/L; reference: 0–1.37 × 109/L). Blood chemistry revealed a mild hypocalcemia (2.17 mmol/L; reference: 2.32–2.92 mmol/L) and a moderately increased creatinine kinase concentration (4048 IU; reference: 0–2678 IU).
All imaging procedures were performed under general anesthesia. An intramuscular injection of medetomidine 0.08 mg/kg and ketamine 10 mg/kg was performed, reaching a sufficient sedation within 10 min which allowed to intubate the trachea. After intubation, the animal received isoflurane, which was administered in 100% oxygen.
The laterolateral radiograph of the cervical vertebral column showed shortening and irregular ventral margins of the seventh cervical vertebral body (C7) and narrowing of the C6/7 intervertebral disk space (Fig. 2). There was a regional dorsal narrowing of the trachea ventral to C6/7 by mild homogenous soft tissue thickening.
Computed tomography (Brilliance, 16 Slice, Philips; 120 kV, 190 mAs, 2 mm slice thickness, 1 mm slice gap) of the cervical vertebral column (Fig. 3) confirmed the radiographical findings. Additionally, the vertebral body of C7 was centrally inhomogeneous and showed a mild step formation at the dorsal and ventral contour and a narrow, irregular, hypodense, dorsoventrally oriented area was present. An involvement of the vertebral canal was not identified.
For further evaluation of the soft tissues within the vertebral canal and the paravertebral soft tissues, pre- and post-contrast (Gadolinium; Clariscan™) MRI was performed during the same anesthesia. T2-weighted sagittal and transversal, pre- and postcontrast T1-weighted dorsal and transversal, T2-weighted fat suppressed (Spectral Presaturation with Inversion Recovery (SPIR)) dorsal and T2*-weighted transversal echo gradient sequences were performed using a 1.0-Tesla open permanent magnet (Philips HFO Panorama, Philips Medical Systems, PC Best, Netherlands). MRI revealed C6/7 nucleus pulposus volume reduction of approximately 50%. The C7 vertebral body showed a heterogeneous low signal intensity in all sequences and an irregular, ill-defined cranial end plate. The vertebral body was isointense to the surrounding musculature in T1-weighted sequence with heterogeneous contrast enhancement. At the level of C7/Th1, a 20 mm long extradural, well-demarcated, heterogeneous mushroom-shaped T2/T2*/SPIR hyper- and T1 isointense, space-occupying lesion was visible in the ventral right-sided aspect of the spinal canal severely dislocating and compressing the spinal cord to the left dorsolateral side (Fig. 4a and b). The material occupied up to 75% of the vertebral canal and showed heterogenous contrast uptake. The left supra- and infraspinatus muscles were showing a stripy, ill-defined delineated hyperintensity in the T2-weighted sequence with contrast enhancement.
These imaging findings were compatible with osteomyelitis, pathological fracture and dorsal and ventral extrusion of inflammatory material (abscess) of the C7 vertebral body. Less probable differentials were primary fracture or vertebral body neoplasia.
After diagnostic imaging, the weaner was euthanized with pentobarbital (Euthasol®) during anesthesia and cerebrospinal fluid was taken atlantooccipitally immediately post-mortem. Analysis of the cerebrospinal fluid revealed a cell count of 103 cells/μl (62% neutrophils, 29% monocytes, 9% lymphocytes) with increased protein concentration (semiquantitative analysis) and negative Pandy reaction. The neutrophilic pleocytosis with increased protein pointed to an inflammatory process [4]. Main differential diagnoses for neutrophilic pleocytosis included suppurative meningitis, spinal trauma, myelomalacia and/or hemorrhage [19].
A CT-guided bone biopsy of C7 vertebral body was performed immediately post-mortem. The microscopic analysis revealed a low cellularity with a granular background containing moderate amounts of debris, smeared cell nuclei, scattered lipid vacuoles and rare pieces of striated myofibers. Intact nucleated cells represented a mixed inflammatory population, consisting predominantly of neutrophils, lower numbers of eosinophils, occasional lymphocytes and macrophages and rarely mast cells. No infectious organisms were found in Gram-stained tissue slides. Morphological diagnosis was a chronic abscess of the C7 vertebral body with a pathological fracture and compression of the spinal cord with associated meningitis and neuritis of the right-sided 6th cervical spinal nerve.
At necropsy, a dorsoventral fracture of the C7 vertebral body was present. The fracture segments were irregular and an accumulation of a moderate amount of pus extending into the spinal canal was detected adjacent to the vertebral fracture. At this location, the spinal cord was severely compressed over a length of 1.5 cm with a reddish discoloration and the dura was adhered lateroventrally to a macroscopically greyish, firm structure. The other organs were macroscopically unremarkable.
Histologically, a severe focal-extensive inflammatory process consisting of numerous degenerated neutrophils surrounded by a high number of macrophages within proliferated fibrous tissue (abscess, Fig. 5) was present in the epidural tissue of the cervical spinal cord and attached to the dura. This inflammatory process involved emerging spinal nerves and paraspinal fat tissue. Within the compressed spinal cord disseminated swollen axons were detected within the white matter. The morphological diagnosis was a chronic abscess of the C7 vertebral body with a pathological fracture and right-sided compression of the spinal cord with associated meningitis and neuritis of the 6th cervical spinal nerves.
Thin slices of the paraffin-embedded vertebral body of C7 were used for PCR and DNA sequence analysis. DNA was prepared from paraffin slices using a previously established protocol [20] followed by column purification using the High pure PCR purification kit (Roche Diagnostics, Rotkreuz, Switzerland). An approximately 360 bp PCR product was amplified with primers 16SUNI-L and 16SRNAV-S using 2 μl of purified paraffin extract and subsequently sequenced according to the protocol described by Kuhnert et al. [21]. Sequences proof-read in both directions were compared against GenBank using BLAST.
A 100% match was found with the A. pleuropneumoniae type strain 16S rRNA gene sequence (Acc.no. NR_115546).