P017 A challenging case of back pain: infection, inflammation or both?

Abstract Introduction Diagnosing axial spondyloarthritis (AxSpA) can be challenging due to its heterogenous presentation and lack of single disease feature on clinical history and examination, laboratory and radiological testing. Furthermore, there are several conditions that can mimic its clinical findings. Among these is spinal tuberculosis which can present with overlapping clinical and radiological features, sometimes leading to a misdiagnosis. Distinction between these two conditions is important to avoid potentially harmful delays in reaching the correct diagnosis and initiating appropriate treatment. While distinct, these conditions can co-exist – as they do in this report. Case description A man in his 30s, of South Asian origin, with no known past medical and family history initially presented with fever, significant weight loss and right shoulder pain. He later developed right upper quadrant pain and progressive lower back pain with associated early morning stiffness. Routine blood tests, including an autoimmune screen, were unremarkable. CT imaging showed a pericardial and liver collection, and bilateral sacroiliitis with a sclerotic lesion in the manubriosternal joint. Serial imaging showed an interval increase in the size of the liver and pericardial collections. His QuantiFERON-TB Gold test was positive. Culture and PCR testing of the pericardial aspirate isolated Mycobacterium tuberculosis and he was commenced on anti-tubercular treatment (ATT). Following this, interval imaging showed a decrease in size of the collections. Despite good response to ATT, his back pain persisted, with some improvement with naproxen. The patient was reviewed by rheumatology. On examination, there was tenderness over the sacroiliac joint (SIJ) and manubrium sterni, and diffuse bilateral paraspinal tenderness in the lower thoracic spine. There was restricted forward and lateral flexion of the spine. The rest of the examination was otherwise unremarkable. HLA-B27 testing was negative, and an X-ray of bilateral SIJ showed grade 3 sacroiliitis. Further investigation through MRI with STIR sequencing demonstrated bilateral sacroiliitis associated with subchondral marrow oedema, and characteristic anterior and posterior corner inflammatory lesions – features of active AxSpA. The patient was commenced on 2-weekly subcutaneous adalimumab injections. After 2 doses of adalimumab, he reported significant improvement in his back pain. At 5-month follow-up, the patient was pain-free and repeat MRI showed complete resolution of the inflammatory lesions. He remains on adalimumab and is regularly followed up in rheumatology clinic for disease activity monitoring and treatment tolerance. Discussion Tuberculosis was initially raised as a differential diagnosis after the liver and pericardial collections were found on CT imaging. This diagnosis was further supported by the presence of constitutional symptoms such as fever and weight loss, and confirmed by isolating Mycobacterium tuberculosis on culture and PCR testing of the pericardial aspirate. In light of these results, the patient was commenced on ATT, and saw significant improvement in his symptoms and resolution of the liver and pericardial collections. He was planned to complete 12 months of ATT to cover bone involvement. However, his symptoms of back and sternal pain persisted despite ATT. The patient reported a history consistent with inflammatory back pain. This, along with the findings of bilateral sacroiliitis and sclerotic lesion, warranted a rheumatology referral and further investigation. HLA-B27 testing was negative; however, an MRI with STIR sequencing demonstrated features of active AxSpA, including the characteristic inflammatory corner lesions. The patient was diagnosed with AxSpA and the decision to start anti-tumour necrosis factor alpha (anti-TNF-α) therapy was made as he had a BASDAI score of 5.8. The British Thoracic Society guidelines state that “patients with active tuberculosis should receive a minimum of 2 months” of full treatment before starting anti-TNF-α therapy. At that stage, the patient was on his 8th month of ATT and was therefore deemed safe to start biologic therapy. This is an interesting and complex case of back pain as it had both an infective and inflammatory cause. The significant response to ATT suggested an infective component to his back pain, whereas the clinical history and radiological findings supported a diagnosis of AxSpA. Several cases of spinal tuberculosis and AxSpA being misdiagnosed as the other have been reported in current literature, but very few cases reported patients diagnosed with both conditions. Key learning points • Diagnosing axial spondyloarthritis (AxSpA) can be challenging due to its heterogenous presentation and other conditions that mimic its radiological and clinical features. • Whilst sacroiliitis can be seen in spinal tuberculosis, this is usually unilateral instead of bilateral. AxSpA should be considered in the presence of bilateral sacroiliitis. • Anterior and posterior corner inflammatory lesions on MRI (the “shiny corner sign”) are characteristic of active AxSpA. When bilateral sacroiliitis is seen on imaging, it is always worth checking for the presence of this sign. • Tuberculosis typically affects the superior aspect of the SIJ, whereas AxSpA usually affects the inferior aspect of the SIJ. Both the superior and inferior aspects were affected in this case. • A confirmed diagnosis of spinal tuberculosis does not rule out the possibility of AxSpA or vice versa. Individual symptoms can have both infective (e.g. tuberculosis) and inflammatory (e.g. AxSpA) causes. • Paying close attention to a patient’s clinical history, and considering their reports of continuing symptoms even in the case of a confirmed diagnosis and otherwise positive response to treatment, is vital to an accurate and complete diagnosis of their condition(s). • Failure to respond or incomplete response to treatment should raise concerns for an alternative diagnosis and warrant further investigation to ensure that accurate diagnosis and treatment decisions are made.