Case Report: Spondylodiscitis as a Differential Diagnosis of Anal Canal Squamous Cell Carcinoma Bone Metastasis

Spondylodiscitis is an uncommon infection affecting the vertebral bodies and surrounding tissues, with an increased incidence in immunosuppressed patients. Back pain is the most common symptom, and early imaging often fails to reveal specific findings. Squamous cell carcinoma (SCC) of the anal canal accounts for 80% of the cases of anal neoplasia, with metastatic disease occurring in 10 to 20% of the cases. We herein report the case of a 61-year-old patient with spondylodiscitis mimicking anal canal SCC bone metastasis. The patient experienced sudden thoracic spine back pain 40 days after salvage chemoradiation for locoregional recurrence. The initial laboratory tests were non-specific for infection, while imaging revealed extensive paravertebral lesions in the thoracic spine. Initially, bone metastasis was suspected, as the patient lacked the common symptoms of infectious disease. However, a peripheral blood culture revealed methicillin-resistant Staphylococcus aureus, and subsequent imaging and pathological findings confirmed spondylodiscitis. Pain investigation in oncological patients should be thorough, considering differential diagnoses such as those of infectious diseases, given the patients' immunosuppression and the risk factors to which they are exposed.