What is your diagnosis?

A three-year-old female Labrador retriever, weighing 40 kg, was referred with a seven day history of malaise followed by a one day history of inability to ambulate on the hindlimbs. The bitch was 49 days pregnant. Clinical examination revealed paraplegia. Pelvic limb and perineal sensation were present and segmental spinal reflexes intact. Examination of the thoracic limbs was unremarkable. The bitch was in good body condition with obvious abdominal enlargement due to the pregnancy. Rectal temperature was 39·2°C. Samples obtained for haematology before referral had demonstrated an increased white cell count (28·5 × 109/l, reference 6·0 to 16·9 × 109/l) and a neutrophilia (19·5 × 109/l, reference 3·3 to 12·0 × 109/l). Serum biochemistry had been unremarkable. Under anaesthesia, a myelogram was performed following lumbar puncture (Fig 1A,B). Cerebrospinal fluid (CSF) was not recovered. A lateral projection of the abdomen was also performed (Fig 2). Lateral (A) and ventrodorsal (B) myelographic projections of the lumbar spine Lateral projection of the abdomen obtained 10 minutes after the myelogram • What abnormalities can be appreciated on the myelogram and the abdominal radiograph? • What are your differential diagnoses? • What further tests would you perform? • How would you treat this case? Answers overleaf • What abnormalities can be seen on the abdominal radiograph and the myelogram? The myelogram demonstrates axial deviation and thinning of the right contrast column indicating a right-sided extradural lesion extending from L2 to the caudal aspect of L4. There is poor contrast filling of the subarchnoid space caudal to L5, especially on the right. Contrast material is present within the central canal and the soft tissues dorsal to the vertebral column at L4–L5 along the injection tract. The lateral abdominal radiograph demonstrates the presence of several foeti. Contrast material can be appreciated within the spinal canal and within the kidneys, ureters and urinary bladder as a result of urinary excretion of contrast agent following the myelogram. An ill-defined soft tissue opacity can be appreciated ventral to the lumbar spine extending from L2 to the sacrum. • What are your differential diagnoses? Differential diagnoses for a right-sided extradural compression at this site include disc extrusion with accompanying haematoma formation, neoplasia, spontaneous extradural haemorrhage and epidural empyema. Differential diagnoses for the soft tissue opacity ventral to the lumbar spine include inflammatory disease, neoplasia, retroperitoneal haematoma and urinoma. • What further tests would you perform? CSF analysis can be useful to detect inflammatory disease. However, CSF was not obtained following lumbar puncture in this dog and hence this was not possible. Advanced imaging such as magnetic resonance imaging (MRI) would have allowed further definition of the extradural lesion and the retroperitoneum but was unavailable. Ultrasonography of the abdomen confirmed the viability of the foeti in this case and revealed fluid accumulation within the retroperitoneal space. Fine needle aspiration, under ultrasonographic guidance if necessary, can be very useful to determine the nature of the fluid from the retroperitoneal space; cytology in this case demonstrated the presence of degenerate neutrophils but bacteria were not identified. • How would you treat this case? A right-sided hemilaminectomy was performed from L2 to L4. A large volume of purulent material was retrieved from the spinal canal. The epidural empyema was noted to communicate with the retroperitoneal space via the intervertebral foramina. Blunt enlargement of the communicating tracts allowed evacuation of approximately 500 ml of purulent material from the retroperitoneal space. Material was obtained for histology and bacteriology from the spinal canal and the retroperitoneal space. Routine closure was performed following copious lavage. Histology of retrieved material was consistent with pyogranulomatous inflammation. No evidence of neoplasia was identified. Bacteriology demonstrated the presence of Pasteurella species which were sensitive to all antibiotics tested. The bitch was prescribed a four week course of clavulanate-potentiated amoxicillin (Synulox; Pfizer) 500 mg twice daily and clindamycin (Antirobe; Pharmacia Animal Health) 300 mg twice daily. At telephone follow-up two weeks after surgery, the owner reported the dog had regained the ability to ambulate and had whelped uneventfully. At four months postoperatively, the owner reported the dog to have maintained normal ambulatory status and had suffered no further health problems. Epidural empyema is an uncommon differential diagnosis for myelopathy in dogs. In a PubMed search, only 10 previous cases were identified in the veterinary literature (Dewey and others 1998, Cherrone and others 2002, Lavely and others 2006). Presenting signs previously reported include lethargy, pyrexia and neurological deficits. Unlike the case reported here, spinal pain is also a common feature (Lavely and others 2006). Peripheral neutrophilia is often apparent on haematology. Myelography allows demonstration of extradural compression which can be focal, diffuse or multi-focal (Lavely and others 2006). Other imaging modalities such as MRI have been reported for diagnosis of epidural empyema in man (Pinkington and others 2003). MRI may also be useful for imaging of epidural empyema in dogs though this has not been reported to the author’s knowledge. CSF analysis would typically show a neutrophilic pleocytosis. However, CSF was not recovered following lumbar puncture in this case. It is unusual to isolate bacteria from CSF, but causative organisms can often be recovered from the surgical site or from urine or blood (Lavely and others 2006). Recovery of organisms from material retrieved from the epidural space under fluoroscopic guidance has also been reported (Dewey and others 1998). A primary cause was not identified in this case. Epidural empyema has been associated with discospondylitis in dogs (Lavely and others 2006) and in man with discospondylitis, systemic infection, spinal injections (Mauer and Kunz 2006) and epidural catheter insertion (Volk and others 2005). Whether the infection in this case originated from the spinal canal or the retroperitoneal space is unclear. This dog is likely to have been marginally immunosuppressed as a result of the pregnancy. Prolonged exposure to progesterone may have diminished leucocyte function and predisposed to seeding of haematogenous infection. Treatment of epidural empyema in both humans and dogs has traditionally consisted of prompt surgical decompression and prolonged courses of antibiotics selected on the basis of bacteriology (Pinkington and others 2003, Lavely and others 2006). More conservative treatment has been used successfully in man consisting of placement of ingress/egress epidural catheters and continuous irrigation with antibiotic solutions over a three day period (Mauer and Kunz 2006). This technique has not been reported in dogs. The prognosis in these cases is fair. Lavely and others (2006) reported five of seven dogs improved after surgery and had a good long-term outcome. In humans, success rates as measured by neurological improvement after surgery range from 66 per cent (Mauer and Kunz 2006) to 100 per cent (Pinkington and others 2003). However, only small numbers of cases have been reported and figures should be interpreted with caution.

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