We report the case of a 52-year-old man with long-standing HLAB27-positive ankylosing spondylitis treated with anti-tumour necrosis factor (TNF) alpha therapy who was admitted to our rheumatology department complaining of increasing lumbar and buttock pain radiating to the posterior thigh, associated with numbness in the leg, gait disturbance and low-grade fever. The clinical picture was initially interpreted as a flare of disease but was not responsive to treatment. A contrast-enhanced spinal MRI was performed with evidence of a diffuse signal abnormality involving the sacroiliac joints and the spine, with evidence of spondylodiscitis of L5 and with a lesion causing L5-S1 root compression and infiltrating the iliopsoas muscle. These findings confirmed the possibility of a reactivation of disease associated with an infectious process. The most frequent causes of infectious spondylodiscitis were excluded, and a biopsy was then performed. Histological analysis revealed a high-grade B-cell non-Hodgkin's lymphoma of the spine. This case highlights how a differential diagnosis of low back pain with neurological symptoms can be particularly troublesome in ankylosing spondylitis and that continuous vigilance is warranted in patients treated with long-term immunosuppressive therapies.
Keywords: Ankylosing spondylitis; Anti-TNF alpha; Lymphoma; Spondylodiscitis.