A 46-year-old male patient with body mass index of 40 kg/m2 presented to our hospital with the chief complaint of "two months history of low back pain with weakness in both legs". On admission, physical examination revealed significant tenderness in the L3-5 intervertebral and paraspinal area, pain and decreased skin sensation in the right calf and dorsum, and weak muscle strength in both lower limbs (right side: grade 3 for tibialis anterior muscle, extensor hallucis longus and triceps surae, and grade 4 for quadriceps femoris; left side: grade 3 for quadriceps femoris, and grade 4 for tibialis anterior muscle, extensor hallucis longus and triceps surae). No obvious kyphosis or scoliosis deformity was found in his whole spine. Laboratory findings and serological examination revealed inflammation. Renal and liver dysfunction was also identified (Table 1). X-ray (Figure 1A and B), magnetic resonance imaging (MRI) (Figure 2A and B) and computed tomography (CT) (Figure 3A and B) scans showed abnormality in his L3-5 lumbar segment. 
Two days after admission, the patient experienced high fever (39.8 C), and complained of abdominal distension, low back pain and oliguria (excretion of about 300 mL of urine per day). Blood culture was then performed. His renal and liver function had further deteriorated. Abnormal myocardial injury markers and myocardial enzyme profiles were observed (Table 1). Tuberculous spondylitis was suspected. Empirical antibiotics (isoniazid 0.3 g, ivggt, qd; pyrazinamide 0.75 g, po, qd; rifampicin 0.45 g, po, qd; and ethambutol, 0.75 g, po, qd) and symptomatic treatments such as diuresis and albumin supplements were given to the patient.
Four days after admission, the patient experienced sudden loss of consciousness and unstable circulation. His inflammation and liver dysfunction were aggravated compared with 2 days before (Table 1). He was transferred to ICU for further treatment. Streptococcus constellatus was identified in his blood culture. Antimicrobial susceptibility tests were then performed. The results showed that isolates from the blood of the patient were susceptible to imipenem, penicillin G, ertapenem, cefepime, cefotaxime, teicoplanin, levofloxacin, chloramphenicol and linezolid, but resistant to erythrocin, tetracycline and clindamycin. During the period in the ICU (lasting for 46 days), systemic antibiotic therapy (imipenem: 1 g, q6h, ivgtt; teicoplanin: 1.2 g, q24h, ivgtt, for the first 3 days, followed by 0.6 g, q24h, ivgtt) and symptomatic treatments such as fluid supplementation, maintenance of water-electrolyte balance, and nutritional support were given to the patient. Lumbar puncture and biopsy of L3-5 disc space tissues were performed on the 31st day after the patient was transferred to ICU. Tissue culture and Mycobacterium tuberculosis (TB)-PCR test results were negative. Pathological results revealed fibrous tissue hyperplasia accompanied by acute and chronic inflammatory cell infiltration; locally, degeneration, necrosis and dead bone formation were also noticed (Figure 4A). Based on all of the test results, TB infection and tumor were ruled out and the patient was finally diagnosed with PS caused by S. constellatus.
After the emergency had been brought under control, the patient was sent back to our department, where obvious swelling in the patient's thigh was noticed (Figure 4B). Approximately 500 mL of brown liquid, i.e. paravertebral pus, which had been generated from the absorption of broken bone and soft tissue in the lumbar spine and descended into the muscle tissue of the thigh along the muscle gap, was suctioned out. No bacteria were found after culture, indicating that the antibiotic therapy had been effective.
A physical examination 78 days after admission revealed tenderness in the L3-5 intervertebral and paraspinal area, hypoesthesia in the inside and outside skin of the right calf, and weak muscle strength in both lower limbs (grade 1 for tibialis anterior muscle, extensor hallucis longus and triceps surae, and grade 3 for quadriceps femoris). His muscle tension was normal. Major lumbar spinal infection and vertebral destruction were noticed on MRI (Figure 2C and D) and CT (Figure 3C and D) scans. Immobilization surgery was planned for the patient; however, he refused surgery for economic reasons. He was discharged from our hospital 53 days later.
Then, 32 days after discharge, the patient returned to our hospital for re-examination. Physical examination showed no tenderness in his whole spine. Hypoesthesia still existed in the inside and outside skin of the right calf. His muscle strength (grade 2 for both right and left side tibialis anterior muscle, extensor hallucis longus and triceps surae, and grade 4 for both right and left side quadriceps femoris) had improved and muscular tension was normal. Laboratory findings were almost normal (Table 1). The MRI results showed that the lumbar spinal infection was alleviated compared with the previous observation (Figure 2E and F). New bone formation and osteosclerotic changes were observed on CT images (Figure 3E and F).