{'fraction_non_alphanumeric': 0.02959621520519309, 'fraction_numerical': 0.011442402904609968, 'mean_word_length': 5.2217659137577, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Spondylodiscitis initially presenting as exudative pleural effusion: A case report and review of the literature

Pleural effusions are associated with a variety of disease states, rendering the differential diagnosis challenging. Spondylodiscitis is an uncommon disease, and its prompt diagnosis can reduce morbidity and mortality. However, an atypical manifestation of the disease, such as pleural effusion, can result in delayed diagnosis. A 76-year-old woman presented with back pain and right pleural effusion. Magnetic resonance imaging revealed paravertebral soft tissue infiltration, with enhancement of bone marrow and intervertebral disk at the T8 and T9 levels, suggesting spondylodiscitis. In patients with exudative pleural effusion, spondylodiscitis may be the cause, so careful analysis of imaging is necessary.


Introduction
Pleural effusions are associated with a wide variety of disorders of the lungs as well as some systemic disorders. Despite a proper diagnostic workup, the cause can remain unknown in up to 20% of cases [1]. The reported incidence of spondylodiscitis in developed world is estimated at 2.2-5.8 cases per 100,000 person years and spondylodiscitis can be a rare cause of exudative pleural effusion [2,3]. Since the initial focus of the investigation for pleural effusion is usually on the pleural diseases, its diagnosis may be delayed in such a case. A careful analysis of early imaging studies can reduce this delay.
Herein, we report a case of exudative pleural effusion caused by pyogenic spondylodiscitis of a thoracic vertebra.

Case presentation
A 76-year-old woman was admitted to our hospital with midthoracic back and left flank pain of three weeks duration. She had no cough, sputum, or other upper respiratory infection symptoms. She had a history of hypertension, controlled with medication, and no other underlying diseases.
On admission, her body temperature was 36.4 • C. Laboratory study showed a white blood cell (WBC) count of 11070/uL, C-reactive protein (CRP) of 9.02 mg/dL, erythrocyte sedimentation rate of 75 mm/h, total protein of 7.6 g/dL, and serum lactate dehydrogenase (LDH) of 144 U/L.
A chest x-ray revealed opacification of the right lower lung field and blunting of the right costophrenic angle, suggesting pleural effusion ( Fig. 1). Chest computed tomography (CT) showed a loculated right pleural effusion with pleural thickening, as well as passive atelectasis in right lower lobe ( Fig. 2a and b). There was neither pneumonic consolidation nor mediastinal lymphadenopathy. Thoracentesis to determine the cause of the pleural effusion yielded exudates with an LDH level of 201 U/L, and a protein level of 5.0 g/L. WBC count was 200/mm 3 , with 58.3% lymphocytes. Adenosine Deaminase was 23.7 IU/L. Gram staining and Ziehl-Neelsen staining were negative. Culture of the pleural fluid demonstrated no growth of a micro-organism, and there were no malignant cells upon cytologic examination. Urinalysis revealed pyuria, and Escherichia coli (E.coli) was yielded in both the urine and blood cultures. Our initial diagnostic impression was urinary tract infection, such as an acute pyelonephritis (APN). Abdomen CT showed no radiologic evidence of APN, and the patients had no complaint of costovertebral angle tenderness. Also the pleural effusion was not sufficiently explained by a consideration of urinary tract infection.
Interestingly, after careful review of the chest CT images, a mild paravertebral soft tissue infiltration was demonstrated at the T8-9 levels ( Fig. 2c and d). Subsequent magnetic resonance imaging (MRI) displayed a high signal intensity on T2-weighted images in the bone marrow and paraspinal soft tissue of T8-9 vertebrae. After intravenous injection of contrast agent, bone marrow and paraspinal soft tissue was enhanced. The enhanced T1-weighted image also demonstrated that enhancement of the paraspinal soft tissue contiguously spread to the adjacent right pleura (Fig. 3). These MRI findings suggested that inflammation due to spondylodiscitis of the thoracic vertebrae had spread to the adjacent right pleura, which may have caused the exudative pleural effusion. Paravertebral soft tissue or involved spinal segment by image-guided biopsy was not obtained. The patient was treated with meropenem and amikacin intravenously, and a chest tube was inserted into the right hemithorax for drainage of the pleural effusion. The patient had an uneventful recovery, her back pain still remained, and her CRP dropped to 1.61 mg/dL on the day of discharge, nearly two months after admission.

Discussion
Pleural effusions accompany a wide variety of diseases of the lungs and pleura as well as systemic disorders. To appropriately manage the pleural effusion, it is important to first determine its cause [1]. The most common causes of exudative pleural effusion include malignancy, tuberculosis, and pneumonia [4]. Less frequently, contiguous spread from adjacent infection, such as a liver abscess or pancreatitis, can give rise to pleural effusions [1].
Incidence of spondylodiscitis or vertebral osteomyelitis is increasing in the developed world and estimated at 2.2-5.8 cases per 100,000 person years [2]. Early diagnosis of spondylodiscitis and appropriate  treatment can reduce hospital stay, morbidity, and mortality. However, non-specific clinical symptoms and signs of this disease make early diagnosis difficult [5].
Although back pain is a common presentation in spondylodiscitis, osteomyelitis is usually not at the forefront of diagnostic considerations. Therefore, diagnosis of the disease often delayed, potentially leading to severe consequences and resulting in long-term neurological impairment [6].
Several cases of spondylodiscitis, or vertebral osteomyelitis, associated with pleural effusion have been reported [3,6-10] ( Table 1). Most of the patients presented with a chief complaint of back pain or thoracic pain; lesions affected by osteomyelitis were at the mid-lower thoracic vertebral levels. CT findings included pleural effusions, vertebral body height loss, and bony destructive change. MRI findings for patients with spondylodiscitis included vertebral signal change, paraspinal infiltration or mass, and decreased disc height.
We reported a case of exudative pleural effusion caused by thoracic spondylodiscitis. The chest CT revealed mild paravertebral soft tissue infiltration at the T8-9 levels; a subsequent MRI demonstrated that the visualized enhancement of the paraspinal soft tissue had contiguously spread to the adjacent right pleura. Therefore, the exudative pleural effusion of the patient may have resulted from the contiguous spread of inflammation due to the thoracic spondylodiscitis. Although the chest CT showed neither destructive change nor decreased vertebral height in our case, careful review of chest CT demonstrated a mild paravertebral infiltration, leading to a suspicion of vertebral osteomyelitis prior to the appearance of bony change or paravertebral soft tissue mass.
CT-guided biopsy for diagnosis of spondylodiscitis is often requested to identify the causative microbial pathogen when clinical and laboratory sign of infection and MRI finding are equivocal. However, CTguided biopsy of the spine is rather invasive procedure and may result in complications such as pain, paresis or hematoma formation [11,12]. Most cases of spondylodiscitis or vertebral osteomyelitis resulted from hematogenous spread from a remote site of infection, most commonly the urinary tract [13]. In present case, although no CT-guided paravertebral soft tissue biopsy or involved spinal segment biopsy was Fig. 3. MRI images of the T8-9 levels. T1 weighted sagittal image (a) shows low signal intensity in the bone marrow of the T8-9 vertebral body (arrows). T2 weighted coronal image with fat suppression (b) shows high signal intensity in bone marrow (arrows) and intervertebral disc (short arrow) and paravertebral soft tissue (arrowheads). Loculated pleural effusion was also demonstrated (asterisks). Fat-suppressed contrast enhanced T1 weighted sagittal and axial images (c-d) show enhancement of bone marrow (arrows) and paraspinal soft tissue (arrowheads). Contiguous enhancement spreading to adjacent right pleura (blank arrowheads) from paravertebral soft tissue is also demonstrated. Phlegmon (blank arrow) causing mild central canal compromise is also noted in the epidural space.
obtained, spondylodiscitis was final diagnosis as considering clinical course, laboratory and culture results.
This case suggests that pyogenic spondylodiscitis can be a rare cause of pleural effusion, and also gives an outline of the usefulness of a comprehensive analysis of imaging to assist in the diagnosing of unexplained exudative pleural effusion.

Conclusion
Spondylodiscitis is a rare etiology of exudative pleural effusion. Careful examination of the thoracic spine on initial imaging studies may be helpful in order to discover the cause of pleural effusion.

Declaration of Competing Interest
The authors report no declarations of interest.