Bilateral Facet Joint Septic Arthritis Induced by Acupuncture: A Case Report Highlighting Diagnostic Challenges and the Importance of Early Intervention

Introduction

Septic arthritis of the facet joint (SAFJ) is a rare condition that is extremely challenging to diagnose. The typical patient presents with nonspecific clinical symptoms, with or without systemic symptoms, such as fever or raised inflammatory markers. SAFJ has significant morbidity and mortality, especially with delayed diagnosis. Hence, a high index of suspicion, early clinical diagnosis and treatment are essential to obtain a favorable outcome.

We present a case of bilateral SAFJ following acupuncture treatment that was initially missed clinically. As septic arthritis of the facet joint almost always presents unilaterally, to the best of our knowledge, this case is the first reported case in literature of septic arthritis involving the facet joints bilaterally following acupuncture. With the increasing prevalence of acupuncture treatment for lower back pain, bilateral SAFJ should be a diagnostic consideration in the patient with worsening chronic back pain.

Case Report

A 53-year-old woman, with pertinent medical history of chronic alcoholism and type 2 diabetes mellitus well-controlled on metformin, was first admitted for worsening atraumatic lower back pain. She had a known history of degenerative back pain and was receiving outpatient orthopedic follow-up. Initial clinical examination raised no red flags. Biochemically, the white blood cell count (WBC) was mildly raised at 11.5×109/L. The platelet count was normal at 165×109/L. The C-reactive protein (CRP) level was raised at 102.9 mg/L. Lumbar spine radiographs at presentation were unremarkable, showing mild background degenerative changes (Figure 1). No bony erosion or endplate sclerosis suggestive of spondylodiscitis or destructive bony processes was identified on these radiographs.

She was treated conservatively with analgesia and was subsequently discharged with an outpatient follow-up appointment. Initial outpatient non-contrast magnetic resonance imaging (MRI) evaluation of the lumbar spine showed degenerative changes and bilateral nonspecific L4-L5 and L5-S1 facet joint effusions, as well as mild nonspecific patchy intramuscular edema in the posterior paravertebral muscles (Figure 2). Clinical examination remained unremarkable, and the patient was still able to ambulate independently. She was continued on conservative management with close outpatient follow-up.

However, the patient’s back pain progressively worsened in the 2 months after her initial admission, with new-onset reduced lower limb power and sensation bilaterally. She was readmitted urgently in view of reduced power (4/5) and sensation (1/2) over the bilateral L5 and S1 distributions. A repeat non-contrast MRI lumbar spine study was performed (Figure 3).

The unenhanced sagittal T2-weighted and STIR MR images of the lumbar spine showed T2-weighted/STIR hyperintense collections at the bilateral L4-L5 facet joints, with adjacent fluid and edema. On the T1-weighted sagittal image, there was bony destruction of the bilateral L4-L5 facet joints, as evidenced by the erosion of bony cortices. On the axial T2-weighted MR image, T2-weighted hyperintense collections were seen in the epidural space as well as the posterior paraspinal muscles, consistent with epidural abscess and paraspinal intramuscular abscesses. Imaging features were consistent with bilateral L4-L5 SAFJ complicated by epidural and posterior paraspinal intramuscular abscesses.

A thorough review of the history at the patient’s readmission revealed that the patient had been attending regular lower back acupuncture sessions for several months leading up to her present readmission.

Computed tomography (CT) was also performed, which confirmed bony destruction of the bilateral L4-L5 facet joints (Figure 4). The patient was listed for emergency surgery and underwent urgent surgical drainage and bilateral lateral facet decompression.

Intraoperative cultures revealed methicillin-sensitive Staphylococcus aureus. Microbiological studies were negative for fungal infection and tuberculosis, and no bacteremia was detected on serial blood cultures. The Infectious Disease service was consulted and advised for at least 6 weeks of antibiotics. The patient was treated with intravenous cloxacillin and subsequently oral cephalexin for a total of 6 weeks, with good clinical improvement.

Postoperatively, the patient recovered well clinically and neurologically, with normalization of biochemical markers. She underwent rehabilitation with physiotherapists and occupational therapists, and was discharged 2 weeks after her operation to a community hospital for further rehabilitation.

Discussion

This is a case of delayed diagnosis of SAFJ, contributed by its rare nature, missed history of acupuncture on initial clinical reviews, and normal screening spine radiographs. This article highlights the insidious nature of SAFJ and its nonspecific clinical presentation, and how clinicians and radiologists should be aware of SAFJ, especially in high-risk patients with a history of acupuncture.

SAFJ is a rare entity and is often missed initially. Although it usually affects older patients in the sixth decade of life, as well as intravenous drug abusers, patients with diabetes, or immunocompromised individuals, SAFJ can also occur across a broad age range, from children as young as 2 years old [1], to young and immunocompetent adults with no risk factors [3–5]. Most cases of facet joint septic arthritis are related to hematogenous spread, with Staphylococcus aureus being the most commonly identified casual microorganism [2–7] in up to 70% of infections. Rarely, it can be caused by direct inoculation, such as through epidural or spinal injections [8,9], or through acupuncture [10].

Patients tend to present with nonspecific clinical symptoms, with or without systemic symptoms such as fever or raised inflammatory markers. Clinical presentation is highly nonspecific; patients can present with acute back pain or even atypically with acute abdominal pain [3]. A significant number of patients may not have constitutional symptoms, such as fever [2,4]. This is especially so for SAFJ through direct inoculation, which may not produce systemic symptoms and signs as is expected from a patient with SAFJ through hematogenous spread. Some patients can present with neurological deficits [11], particularly when there is epidural space extension, or when the exiting or traversing nerve roots are compressed or directly involved. Often, pain can be the only presenting symptom [2,12].

Given the nonspecific presentation of SAFJ, it then becomes paramount to ask for a history of direct inoculation, such as acupuncture or epidural and spinal injections, in patients presenting with back pain. Patients with chronic lower back pain are increasingly receiving injections or acupuncture for pain relief in the outpatient and community settings as these practices become increasingly prevalent globally. This group of patients with chronic lower back pain is also precisely the population in which iatrogenic SAFJ, with its nonspecific presentation, can arise insidiously. For these patients, clinicians need to have a high index of suspicion for iatrogenic SAFJ and take a detailed clinical history for any acupuncture or back injections.

Biochemical inflammatory markers, such as CRP and erythrocyte sedimentation rate (ESR), are often readily available in most outpatient and community settings, and are often raised in cases of SAFJ. However, there have been cases in which CRP and ESR levels are normal [2]; WBC levels have also been reported to be raised in only about 50% of patients [3]. Of note, normal inflammatory markers do not exclude the presence of SAFJ. In our case, there were mildly raised inflammatory markers that were not further evaluated clinically due to the patient remaining clinically well and afebrile. Taken alone, mildly raised inflammatory markers are nonspecific. That being said, a properly elicited clinical history of direct inoculation and recent acupuncture should raise the possibility of SAFJ and lead the clinician to early evaluation with further imaging for SAFJ.

Contrast-enhanced MRI remains the criterion standard for the evaluation of SAFJ. MRI findings can appear as soon as 2 to 5 days after symptom onset [1–3], compared with 2 weeks for CT and 6 weeks for radiographs. It is important to note that the absence of bony erosion or destruction on spine radiographs does not exclude the presence of SAFJ. Early MRI should be obtained when there is persistent pain and in the presence of risk factors (eg, recent acupuncture or immunosuppressed states such as long-term steroid intake or chronic alcohol use).

It is worth noting that SAFJ is typically associated with unilateral facet joint involvement. Nearly all cases reported in the literature thus far have been unilateral SAFJ [7], which are commonly associated with bacteremia and hematogenous spread [2–5,7,13]. Bilateral SAFJ should prompt suspicion for acupuncture as a possible cause. In acupuncture treatment for lower back pain, needles are often placed bilaterally in acupoints at the bilateral paraspinal regions, most commonly at the BL20, BL23, BL24, and BL25 acupoints [14,15]. For example, the BL25 acupoint is located 1.5 cun (5 cm) lateral to the inferior border of the L4 spinous process, in close proximity to the L4-L5 facet joint. It is conceivable that the facet joint could be transgressed when accessing such an acupoint incorrectly, such as using an incorrect needle length, placing the needle at the wrong needle depth, or adopting an incorrect angle of approach.

While acupuncture itself may have conceivably contributed to the findings of facet joint effusions and intramuscular edema in the posterior paravertebral muscles, SAFJ, however, cannot be excluded in the context of worsening back pain and raised inflammatory markers. In our case, the findings of bilateral facet joint effusions on the initial MRI, in the context of raised inflammatory markers and recent acupuncture, should have raised suspicion for early bilateral SAFJ. This may be a diagnostic pitfall for clinicians and radiologists alike, who are generally more familiar with unilateral SAFJ.

It is our opinion that early empirical antibiotics should have been initiated at the first presentation. This patient had risk factors for immunosuppression (diabetes, chronic alcoholism), and at initial presentation the patient also had worsening chronic back pain, raised inflammatory markers, and bilateral facet joint effusions on MRI. These features raise the possibility of early SAFJ. With the additional clinical history of recent acupuncture and direct inoculation, SAFJ would have been a strong diagnostic consideration. Given the high diagnostic probability of SAFJ and the high morbidity associated with SAFJ, parenteral empiric antibiotics should have been initiated as early as possible.

Treatment of SAFJ includes a course of antibiotics for at least 6 to 8 weeks. For cases with sizeable paravertebral abscesses, percutaneous or open drainage may be necessary, especially when there is neurological compromise [12,13], such as that in our patient who underwent surgical drainage and bilateral facet decompression for acute bilateral lower limb weakness and numbness. Response to treatment can be assessed with serial inflammatory markers and a follow-up MRI study to ensure resolution of facet joint effusions and periarticular collections.

Conclusions

SAFJ has significant morbidity and mortality, especially with delayed diagnosis. With the increasing prevalence of acupuncture treatment for lower back pain, bilateral SAFJ should be a diagnostic consideration for patients with worsening chronic back pain. Detailed clinical history is key; this, as well as a high index of suspicion, early evaluation and treatment, are essential to obtain a favorable outcome.