Presumed septic sacroiliitis in a puppy with unilateral hind limb lameness and sciatic nerve neuropathy

Abstract A 5‐month‐old female entire Dachshund presented with an acute onset of left hind limb lameness following intense play. There were concurrent intermittent neurological deficits in the left hind limb, and pain in the lumbosacral region and on dorsal flexion of the tail. Computed tomography (CT) imaging revealed an asymmetric widening of the left sacroiliac joint with loss of cortical margins, accompanied by mild osteolytic changes of the adjacent ilium and sacrum highly suggestive of septic sacroiliitis. There was also perilesional steatitis in the region of the sciatic nerve. An 8‐week course of antimicrobial therapy was prescribed. Complete resolution of all clinical signs was noted at a 7‐month follow up. Sacroiliitis should be considered as a differential for unilateral hind limb lameness with or without intermittent sciatic neuropathy in a puppy in the absence of other orthopaedic conditions.


| INTRODUC TI ON
The sacroiliac joint is composed of a synchondrosis component craniodorsally, and a synovial component caudoventrally. The osseous surfaces of the synchondrosis component are uneven and variably concave, and the synovial component is smooth. The sacroiliac joint connects to the wings of the ilium and the sacrum and is stabilised by dorsal and ventral sacroiliac ligaments. The ventral branches of spinal nerves L6 to S2 travel along the ventral aspect of the sacroiliac joint to form the lumbosacral plexus (Evans & de Lahunta, 2013). The function of the sacroiliac joint is to support the caudal portion of the body, and transmit propulsive forces from the hind limbs to the spine (Breit & Kunzel, 2001). The synovial part of the joint allows for rotation and translation of the ilium relative to the sacrum. The synchondrosis part stabilises the joint, and together with the sacroiliac ligaments, restrict craniocaudal and dorsoventral movement of the ilium relative to the sacrum (Breit & Kunzel, 2001).
Septic arthropathy of the sacroiliac joint is rare in dogs and is not well described in the veterinary literature. In humans, sacroiliitis is uncommon and can be caused by various aetiologies including trauma, infection, degenerative disorders and inflammatory processes (Kanna et al., 2019). Non-specific physical examination findings may make achieving a diagnosis difficult and thus delay appropriate treatment. The most common presenting sign is pain localised to the lumbosacral region. Radiographic studies of the caudal spine and hind limbs are often normal in the early stages of the disease. Advanced imaging such as a CT scan or Magnetic Resonance Imaging (MRI) are required to evaluate the sacroiliac joint.
This case report describes the diagnosis of presumed septic sacroiliitis including pertinent imaging findings, treatment and prognosis in a puppy. DOI: 10.1002/vms3.519

C A S E R E P O R T
Presumed septic sacroiliitis in a puppy with unilateral hind limb lameness and sciatic nerve neuropathy 2 | GOH and HOUSE

| C A S E HIS TORY
A 5-month-old female entire Dachshund presented with an acute 4-day history of back pain and difficulty rising on her hind limbs. She was known to be an extremely active and energetic dog. Three days prior to presentation to her regular veterinarian she was running and playing enthusiastically at the beach. The following day it was noted she was reluctant to exercise and collapsed in her hind limbs whenever she attempted to stand. She was up to date with vaccinations and anti-parasitic preventatives and had no prior medical history.
She was subsequently referred to the surgical department for further investigation.
On physical examination, there was a mild left hind limb lameness and a mild pain response on flexion of her tail dorsally. There were also equivocal neurological abnormalities in her left hind. There were no other abnormalities detected on examination.
Survey radiographs were obtained under general anaesthesia. A lateral projection of the lumbar spine including the hip joints and the proximal coccygeal region, mediolateral and caudocranial projections of the hocks and stifles, and a hip extended and a splayed ventrodorsal projection of the hip joints were performed. On the hip extended ventrodorsal radiographic view (Figure 1), the margins of the left sacroiliac joint were subtly irregular and less well defined as compared to the right sacroiliac joint. The remainder of the radiographs were consistent with a skeletally immature dog and there were no other abnormalities identified ( Figure 1). Additionally, the hip joints were assessed for laxity using the Ortolani test with the dog in left and right lateral recumbency respectively (Ortolani, 1976).
The hip joints were assessed for luxation in both craniodorsal and caudoventral directions. The tests were negative, and subluxation was not able to be induced. It was elected to trial a short course of Meloxicam 0.1 mg/kg (Metacam; Boehringer Ingelheim) per os once daily for a week.
There was a mild response observed initially in terms of her pain levels. However, she quickly re-presented a few days later with deterioration in clinical signs and worsening of pain. She remained otherwise systemically well in herself. On presentation she was non- Arthrocentesis of both stifles and hocks were performed. Cytology analysis of the joint fluid was performed by a board-certified veterinary pathologist and were reported to be normal with no microorganisms seen.
Treatment was commenced for a potential left sacroiliac septic arthropathy. An 8-week course of amoxycillin/clavulanic acid 12.5 mg per os twice daily was prescribed, and meloxicam was continued as previously prescribed for another week. It was advised to restrict exercise for 2 weeks. Following commencement of antimicrobial therapy there was an immediate response with improvement of lameness and pain within 12 hr. A 2-week recheck found no lameness or pain and Meloxicam was discontinued. A revisit a week after the course of antibiotics found no abnormalities on physical examination, and owner reported that she was back to her normal demeanour. A 7-month follow up found complete resolution of signs with no recurrence and a full return to normal function.
F I G U R E 2 A transverse (a) and dorsal (b) multiplanar reconstruction CT image at the level of the sacroiliac joint using bone windowing (window width, WW = 2,500, window level, WL = 500). There is asymmetric widening of the left sacroiliac joint with an irregular loss of sharp cortical margins with evidence of mild bony destruction of the ilium, and to a lesser extent, the lateral aspect of the sacrum (block arrows). There is subtle amorphous periosteal proliferation of the left ilium immediately caudal to the sacroiliac joint (curved arrow). Cd, caudal; Cr, cranial; D, dorsal; L, left; R, right; V, ventral F I G U R E 3 A post-intravenous contrast transverse (a) and dorsal (b) multiplanar reconstruction CT image of the sacroiliac joint using soft tissue windowing (window width, WW = 320, window length, WL = 40). There is contrast enhancement of the soft tissue immediately adjacent to the left sacroiliac joint (arrow). Cd, caudal; Cr, cranial; D, dorsal; L, left; R, right; V, ventral

| D ISCUSS I ON
The challenges surrounding a septic arthropathy invariably lies in reaching a definitive diagnosis. The presumptive diagnosis of a bacterial arthropathy was made in this case primarily based on imaging findings, and the drastic improvement with antimicrobial therapy.
Furthermore, the worsening of clinical signs despite a course of NSAIDs suggests that the source of the lameness and pain was not solely just inflammatory in origin. Amoxycillin/clavulanic acid was chosen for its broad-spectrum activity, and its activity against the commonly incriminated bacteria species in a septic arthritis, including Staphylococcus intermedius, Staphylococcus aureus, and beta-haemolytic Streptococci species (Johnston & Tobias, 2017).
Staphylococcus canis appears to be the most commonly isolated bacteria in congenital or neonatal spread of septic arthritis (Johnston & Tobias, 2017 (Johnston & Tobias, 2017). Majority of cases present as an monoarthropathy. Occasionally, a polyarthropathy may occur in an immature or immunocompromised patient. Puppies may develop bacterial polyarthropathy secondary to omphalophlebitis, streptococcal pharyngitis or uterine or mammary infections in the mother.
A congenital or neonatal spread was considered given the young age of this puppy. However, the lack of other systemic signs made this unlikely. Additionally, all other puppies in the same litter, as well as her mother, were reportedly clinically normal with no medical history. Septic sacroiliitis was recently described in a 4-month-old male entire Boxer that developed sacroiliitis as a direct extension of an intrapelvic abscess (Slater et al., 2019). This dog also had a concurrent history of chronic diarrhoea refractory to multiple courses of metronidazole therapy. In contrast to the case described here, there were no known risk factors for a septic sacroiliitis. Exercise related trauma to the sacroiliac joint, though not previously documented as a predisposing factor leading to septic arthropathy in dogs, may have played a part in the pathogenesis in this case. This dog was playing vigorously the day prior to the onset of lameness, which could have caused a degree of trauma and inflammation to the sacroiliac joint.
It is possible that with inflammation of the sacroiliac joint, there was interrupted tissue integrity and hypoperfusion and reduced host defence mechanisms, which may have led to the subsequent development of a septic sacroiliitis.
The technique of sampling the sacroiliac joint is not well described in the literature. Arthrocentesis of the sacroiliac joint was attempted in this dog however given the sample was non-conclusive F I G U R E 4 A post-intravenous contrast transverse (a) and dorsal (b) multiplanar reconstruction CT image of the sacroiliac joint using soft tissue windowing (window width, WW = 320, window length, WL = 40). There is evidence of left sacroiliac joint swelling, and perilesional steatitis and fat stranding (arrow) in the region of the left sciatic nerve and nearby blood vessel (*). As a result, the sciatic nerve and blood vessel (*) are being displaced medially. Cd, caudal; Cr, cranial; D, dorsal; L, left; R, right; V, ventral | 5 GOH and HOUSE it was elected not to proceed with culture and sensitivity testing. It was possible that the sample was collected from the synchondrosis component of the joint which resulted in a relatively low cellular yield. Ultrasound-guided sacroiliac injection has been reported to be an effective means to localise and treat pain due to sacroiliac disease in people and horses (Cousty et al., 2008;Pekkafahli et al., 2003).
The feasibility and accuracy of an ultrasound-guided sacroiliac joint injection technique was evaluated in a cadaveric study (Jones et al., 2012). Sonoanatomic landmarks were the L7/S2 articular process joints, iliac wing, sacral wing, sacral lamina and the median sacral crest. The transducer was placed caudally, and the sacroiliac joint space is visualised as a triangular, hypoechoic indentation at the junction between the iliac and sacral wings. A 22 gauge, 40-or 60mm spinal needle was directed cranioventrolaterally and advanced towards the joint space. The maximum volume that could be injected without resistance was 0.5 ml. While the technique was good for injecting into the synchondrosis portion of the sacroiliac joint, it was fair to poor for injecting into the synovial portion of the sacroiliac joint (Jones et al., 2012). With extrapolation of the results of this study, ultrasound-guided sampling of the sacroiliac joint via this technique may also be attempted, however sampling of the synovial component of the sacroiliac joint may still prove difficult. CT-guided sacroiliac joint sampling in people with suspect infection has been described using percutaneous aspiration of the joint, lavage aspiration, bone biopsies of the sacrum, ilium or both, and biopsies of the sacroiliac joint or adjacent soft tissue (Knipp et al., 2018). A posterior or anterior approach to the joint was chosen based on feasibility, technical difficulty and whether the anterior or posterior aspect of the sacroiliac joint was more distended on CT. The overall sensitivity and specificity were reportedly 54% and 86% respectively (Knipp et al., 2018). Aspiration was found to have a higher sensitivity than that of biopsy, followed by lavage aspiration (Knipp et al., 2018). CTguided aspiration of the sacroiliac joint in dogs may be explored as an alternative. The accuracy and reliability of sampling of the sacroiliac joint under the guidance of the various imaging modalities, and the sensitivity and specificity of aspiration, lavage aspiration or biopsy have yet to be evaluated in dogs.
Lameness in this dog was attributed to septic sacroiliitis and potential sciatic nerve irritation. Delayed conscious proprioception in the left hind limb had been intermittently observed. Septic sacroiliitis and the surrounding perilesional steatitis likely contributed to a degree of sciatic nerve irritation and hence sporadic neurological deficits. Although screening radiographs performed raised the suspicion of whether the patient's clinical signs were associated with potential pathology in the left sacroiliac joint, these changes were overall subtle, and a diagnosis could not be convincingly made solely based on these findings. Cross-sectional imaging techniques are the preferred diagnostic imaging modalities to evaluate the lumbosacral region.
CT findings in this dog was similar to that previously reported for sacroiliitis (Forbes et al., 2019). CT scan of a dog with Brucella canis sacroiliitis and discospondylitis found variable widening of the sacroiliac joint with adjacent regions of subchondral sclerosis, and regions of decreased cortical delineation adjacent to the sacroiliac articulations, in addition to the changes within several lumbar vertebral end plates consistent with discospondylitis. MRI has also been used to evaluate the sacroiliac joint in a case report involving two dogs (Slater et al., 2019). Sequences acquired included T2-weighted fastspin echo in sagittal and transverse planes, T1-weighted fast-spin echo in transverse and sagittal planes, with and without fat saturation, pre-and post-contrast medium administration, dorsal short tau inversion recovery and dorsal T2 IDEAL (Slater et al., 2019). Changes observed include an irregular and widened joint, joint effusion, oedematous bone marrow and periarticular soft tissue structures, and contrast enhancement of the fibrous and cartilaginous aspects of the sacroiliac joint space (Slater et al., 2019).
The main limitation of this case report lies in obtaining a definitive diagnosis of a septic sacroiliitis. Ideally a diagnosis was made on culture results of the sacroiliac joint. Obtaining a diagnostic sample of the sacroiliac joint is shown to be challenging even with fluoroscopic or ultrasonic guidance. Given the rapid response to antimicrobial therapy, repeat sampling or obtaining blood cultures were deemed unnecessary. Repeat CT at follow up may have been useful to document changes to the sacroiliac joint. However, the risk of additional radiation exposure to the puppy, and given the complete resolution of clinical signs, it was determined that repeat imaging was not indicated.
Sacroiliitis should be considered as a differential for unilateral limb lameness, lumbosacral pain and sciatic neuropathy in the affected limb. Heavy exercise may be an inciting cause of sacroiliitis.
An extended duration of antimicrobial therapy is recommended, particularly if there are indications of adjacent osteomyelitis on imaging studies. Prognosis appears to be excellent with appropriate treatment.

CO N FLI C T O F I NTE R E S T
The authors declare no conflict of interest related to this study.

PE E R R E V I E W
The peer review history for this article is available at https://publo ns.com/publo n/10.1002/vms3.519.