Septic arthritis of unilateral lumbar facet joint with contiguous abscess, without prior intervention

Abstract

A 40-year-old female patient presented with persistent severe back pain radiating to the right leg, abdominal pain and constipation. Other clinical symptoms included nausea, vomiting and high-grade fever. Clinical examination showed generalised abdominal and lower back tenderness. There was no sensory loss or motor weakness in lower limbs, however investigations showed raised inflammatory markers. Radiographs of the lumbar spine and hip joint were normal. MRI revealed a septic arthritis of the right L3/4 facet joint, associated with a large abscess extending anteriorly to the right paraspinal muscles and posteriorly into the right posterolateral aspect of the epidural space in the central spinal canal, with moderate compression of the dural sac. Unlike any other reported similar case, this septic arthritis developed without prior medical intervention. The patient was treated successfully with ultrasound guided drainage of the facet joint/abscess and antibiotics.

Background

Septic arthritis of a lumbar facet joint is a rare cause of lower back pain. It is occasionally associated with an epidural abscess,¹ although these are also rare, with an estimated incidence of 0.2–2.0/10 000 hospital admissions.²

A high index of clinical suspicion is required for early diagnosis and cost effective treatment. Normally septic arthritis of a unilateral facet joint is associated with previous medical intervention, such as epidural injections or acupuncture.³ However, in this case, the patient had never undergone any such procedure; an extensive literature search has shown no reported cases a similar situation. The case is also unusual in that spinal epidural abscesses have a peak incidence in the sixth and seventh decades of life,² so the patient in this case is uncharacteristically young.

Case presentation

The patient was a 40-year-old female ex-injecting drug user. She had been suffering from severe back pain radiating to the right leg for 9 days prior to admission, for which she was being treated with tramadol. The patient only presented to the accident and emergency department after she developed abdominal pain and constipation. Other clinical symptoms included nausea, vomiting and high-grade fever. Medical history was of an appendectomy as a child; and asthma, for which she was on salbutamol and beclomethasone. The patient was also taking diazepam, and had being using oral methadone for 5 years. She was not diabetic and has no other medical history of note.

Investigations

Clinical examination showed generalised abdominal and lower back tenderness. There was no sensory loss or motor weakness in lower limbs, though there was pain on movement, especially on flexion of the right hip and knee. Clinical investigations showed raised inflammatory markers (C-reactive protein (CRP) 316). Radiographs of the lumbar spine and hip joint were normal (figures 1 and 2). Chest radiographs were normal, urine was clear of infection, and blood cultures showed no infection. MRI revealed a septic arthritis of the right L3/4 facet joint (figures 3–11), associated with a large abscess extending anteriorly to the right paraspinal muscles and posteriorly into the right posterolateral aspect of the epidural space in the central spinal canal, with moderate compression of the dural sac (figures 12–18). The intervertebral discs were normal. No intradural abnormality was seen and the distal spinal cord was normal. This abscess was caused by Gram-positive Cocci bacteria, Staphylococcus aureus.

Figure 1.

Anteroposterior lumbar spine x-ray–No abnormalities shown.

Figure 2.

Lateral lumbar spine x-ray–No abnormalities shown.

Figure 3.

MRI axial T1 fat sat GAD 2–Shows rim enhancement of the facet joint abscess.

Figure 11.

MRI cor T2 fat sat GAD 3–Shows rim enhancement of abscess which extends into the adjacent muscle.

Figure 12.

MRI sag T2 best 2–Showing facet joint abscess with extension anteriorly into the epidural space, posteriorly into the erector spinae muscles.

Figure 18.

MRI sag T2 fat sat best 3–Showing facet joint abscess with extension anteriorly into the epidural space, posteriorly into the erector spinae muscles.

Figure 4.

MRI axial T1 fat sat GAD 4–Shows rim enhancement of the facet joint abscess.

Figure 5.

MRI axial T1 fat sat GAD–Shows rim enhancement of the facet joint abscess and shows abscess extension into the epidural space, with resulting canal stenosis and displacement of the dural sac.

Figure 6.

MRI axial T2 best large 2–Shows septic arthritis of the facet joint with extension anteriorly into the epidural space, compressing and displacing the dural sac. Extension posteriorly into the erector spinae muscles.

Figure 7.

MRI axial T2 best large–Shows septic arthritis of the facet joint with extension anteriorly into the epidural space, compressing and displacing the dural sac. Extension posteriorly into the erector spinae muscles.

Figure 8.

MRI axial T2 2–Shows septic arthritis of the facet joint with extension anteriorly into the epidural space, compressing and displacing the dural sac. Extension posteriorly into the erector spinae muscles.

Figure 9.

MRI axial T2 3–Shows septic arthritis of the facet joint with extension anteriorly into the epidural space, compressing and displacing the dural sac. Extension posteriorly into the erector spinae muscles.

Figure 10.

MRI cor T2 fat sat GAD 3 larger–Shows rim enhancement of abscess which extends into the adjacent muscle.

Figure 13.

MRI sag T2 best 3–Showing facet joint abscess with extension anteriorly into the epidural space, posteriorly into the erector spinae muscles.

Figure 14.

MRI sag T2 best 4–Showing facet joint abscess with extension anteriorly into the epidural space, posteriorly into the erector spinae muscles.

Figure 15.

MRI sag T2 best 5–Showing facet joint abscess with extension anteriorly into the epidural space, posteriorly into the erector spinae muscles.

Figure 16.

MRI sag T2 best–Showing facet joint abscess with extension anteriorly into the epidural space, posteriorly into the erector spinae muscles.

Figure 17.

MRI sag T2 fat sat best 2–Showing facet joint abscess with extension anteriorly into the epidural space, posteriorly into the erector spinae muscles.

Differential diagnosis

Patients presenting with generalised back pain, fever and occasionally nausea and elevated inflammatory markers (erythrocyte sedimentation rate (ESR) and CRP), may be suffering from septic arthritis of a lumbar unilateral facet joint. However, the symptoms and populations at risk are nearly identical to that of spondylodiscitis. Facet joint septic arthritis must be considered when patients present with unilateral symptoms, or show a more rapid symptom progression (4 weeks) compared to the typical presentation of the more common spondylodiscitis (2–3 months).⁴ Other differential diagnoses include non-pyogenic infection such as tuberculosis, degenerative or inflammatory arthritis and malignancy. Lytic or destructive lesions involving the posterior elements are most often neoplastic in aetiology.⁵ It is reported that severe neurological impairment is more common with spinal infection (39%), than with tumours (14%).⁶

Treatment

The patient underwent ultrasound guided drainage of the facet joint and associated abscess. She was also treated with intravenous and oral antibiotics. Initially the antibiotic used was flucloxcillin (dosage and duration, oral or intravenous?) however, after the patient developed an apparent reaction to this with skin excoriations, it was stopped and she was started on ceftriaxone and rifampicin.

Outcome and follow-up

The patient recovered well from the initial symptoms though she did develop a urinary tract infection before she was discharged. She was followed up regularly by her general practitioner, and due to the fact that there was no recurrence of her symptoms, a follow-up MRI was not considered necessary.

Discussion

Septic arthritis is most commonly seen in larger peripheral joints,⁵ but occasionally reported in facet joints. The vast majority of these cases are reported in the lumbar spine (86–97%),⁵ and current literature suggests two main causes. The majority of cases arise from haematogenous spread from infection elsewhere in the body (72%).⁵ Alternatively, the cause can be iatrogenic, caused by procedures such as: corticosteroid injection⁷; epidural injection; and acupuncture.³ Other suggested causes are joint surgery, or secondary infection due to penetrating injuries.⁸ However, in our case, the septic arthritis and associated abscess developed without the patient having undergone any procedure in this region. Furthermore, blood cultures, urine and chest radiographs showed no sign of bacterial infection. The patient showed no sign of infection elsewhere in the body. This apparently isolated development of septic arthritis/abscess in the lumbar facet joint is unreported in medical literature to our knowledge. This case also intends to highlight the use of ultrasound in both diagnosing and treating this problem, a technique that appears to be undervalued in some literature.

Although the mortality from spinal epidural abscess has improved from that described in the early reports, it has remained surprisingly consistent over the past several decades, at about 14%,⁹ most likely due to delayed treatment. As such, a high index of clinical suspicion needs to be maintained for diagnosis at the earliest possible stage.^1–3

The exact pathogenesis of septic arthritis is multifactoral, and depends on both host factors and risk factors. Defects in the host immune system, specifically complement and/or reticuloendothelial systems are believed to inhibit the host’s ability to contain gonococcal infections. The patient in this case may have suffered from an impaired immune response due to past drug use, perhaps explaining the seemingly spontaneous infection in the unilateral facet joint. Risk factors, aside from being over 60, include degenerative joint disease, rheumatoid arthritis and corticosteroid therapies.¹⁰ Indeed people with rheumatoid arthritis are 10 times more likely to develop septic arthritis.¹¹

Virtually every bacterial organism has been reported to cause septic arthritis. The microorganism responsible in each case often depends on host factors and the method of infection; however, the most common aetiological agent of all septic arthritis cases in Europe and all non-gonococcal cases in the United States is S aureus.¹⁰

The patient in this case presented with the classic symptoms of septic arthritis in this region: generalised lower back pain, fever, nausea and general malaise. Septic arthritis of a unilateral lumbar facet joint should be considered on the strength of these symptoms, and a thorough clinical history is important in diagnosis on this disease.

Epidural abscess formation associated with septic arthritis of a unilateral facet joint, as in this case, is rare. Reported cases are scarce,^{7 12} and the ones that are published, all describe patients who have undergone facet joint injections, and presented with subsequent lower back pain and fever.

There are a number of diagnostic methods to confirm the diagnosis. Serologic tests such as ESR and CRP are the routine initial investigations, and are elevated in the majority of cases.⁴ Such tests are quite sensitive, but specificity is relatively low.⁸ Isolation of the pathogen from aspirated joint fluid can be used diagnostically and to target antibiotic therapy.

Anterio-posterior and lateral radiographs of the lumbosacral spine are part of the first line investigations. However, in many cases, including this one, radiographs show no evidence of septic arthritis (figures 1 and 2).^{1 4} After longer periods, ranging from weeks to months radiographs may show loss of cortical density with reduction of disc space height. Such imaging should not be regarded as conclusive in patients with identical symptoms.

MRI is considered the diagnostic imaging procedure of choice, being both a highly sensitive and a highly specific method for identifying infection of the lumbar facet joint by most similar reported cases.^{1 2 6–8} It should be considered early in the series of investigation when a patient presents with severe lower back pain, especially when combined with any of the other symptoms described. MRI permits early diagnosis of infection and provides direct visualisation of the spinal cord, subarachnoid space, extradural soft tissues and spinal column without the use of intrathecal contrast material.¹³

Radionuclide imaging may also be used to good effect in patients who cannot undergo MRI. Bone-gallium imaging has given results comparable to those of MRI.¹⁴ In addition to enhancing the specificity of the bone scan, gallium is useful for detecting the abscesses that can accompany septic arthritis.

Some literature suggests that the application of diagnostic ultrasound in the adult spine is inadequately studied and the evidence does not support its routine application for these purposes at this time.¹⁵ However, in this case the abscess showed up clearly on ultrasound (figure 19). Furthermore, the percutaneous drainage of the abscess under ultrasound guidance was a straightforward and satisfactory procedure. In this, authors experience that the use of ultrasound to guide procedures in this region is underused in modern medicine.

Figure 19.

Ultrasound demonstrating abscess collection in the deep soft tissues and muscle.

CT provides structural details in the bone and intervertebral disc, but MRI is the superior imaging test for diagnosing infections earlier and more accurately.¹⁶ Myelography or CT myelography can be effective in diagnosis of extradural spinal compression or blocking due to spinal epidural abscesses but entails the risk of seeding infection into the subarachnoid space.¹⁷

As stated before, facet joint infections can be complicated by abscess formation in the epidural space or in the paraspinal muscles.¹⁶ Percutaneous drainage of the involved joint/abscess has a higher rate of success (85%) than treatment with antibiotics alone (71%),¹⁶ and although the difference is not significant (p=0.37),¹⁸ using both as in this case is what is generally recommended in the literature. In cases with severe neurologic impairment, surgical incision/debridement should be considered.⁶

The incidence of facet joint septic arthritis is increasing,⁶ likely factors include increasing average age and higher numbers of immunosuppressed patients. With improved imaging technology, availability of MRI and heightened awareness, this rare infection can be diagnosed early, however, the growth in resistant strains of bacteria complicates the situation. Some cases of septic arthritis that develop into abscesses can even result in death,^{19 20} a high index of clinical suspicion can prevent such mortality.

In conclusion, septic arthritis, with or without an associated abscess should be considered in patients who present with similar symptoms as ours. The vast majority of patients with this condition have undergone facet joint injection, other invasive procedures in the lumbar region, or have infection else where in the body. However, this case report demonstrates that these are not absolute prerequisites. Particular attention should be paid in patients such as ours, who are injecting drug users, as this would appear to be a risk factor in patients otherwise unlikely to develop the condition. Combined antibiotics and ultrasound guided percutaneous drainage of an abscess can be a successful form of treatment in such cases.

Learning points.

• ▶Septic arthritis of a lumber facet joint may occur in patients who have not had interventional procedures in the region, though this is extremely rare.
• ▶Septic arthritis of a lumbar facet joint, associated with an abscess should be considered in patients presenting with lower back pain, fever and nausea.
• ▶Radiographs do not always show abscesses in this region. MRI, CT and ultrasound are the diagnostic imaging techniques of choice.
• ▶Ultrasound can be used to good effect to diagnose and aspirate septic arthritis/abscess of a lumbar facet joint.