When Fever Strikes Twice: A Case Report of <em>Streptococcus pneumoniae</em> Myelitis with Delayed-Onset Reactive Arthritis

Abstract Background: Streptococcus pneumoniae is a well-known pathogen responsible for respiratory and invasive diseases; however, central nervous system (CNS) involvement in the form of bacterial myelitis is exceedingly rare, particularly in immunocompetent adults. Moreover, the association between pneumococcal infections and reactive arthritis is scarcely documented. We report an unusual case of pneumococcal myelitis complicated by reactive arthritis in an elderly patient with no evident immunosuppression. Case Presentation: A 68-year-old man with a medical history of hypertension, benign prostatic hyperplasia, multiple disc herniations, and a resected pancreatic neuroendocrine tumour presented to the emergency department with acute urinary retention and fever (38.5 °C). The neurological examination revealed lower limb weakness and decreased deep tendon reflexes. Spinal magnetic resonance demonstrated T2 hyperintense lesions suggestive of longitudinally transverse myelitis. Cerebrospinal fluid (CSF) analysis showed pleocytosis with elevated protein levels; the polymerase chain reaction (PCR) test resulted positive for Streptococcus pneumoniae. The patient received intravenous antimicrobial and corticosteroid therapy with partial neurological improvement. Within days, he developed acute monoarthritis of the right ankle. Joint aspiration revealed sterile inflammatory fluid, negative for crystals and cultures, supporting a diagnosis of reactive arthritis. The articular symptoms resolved with the use of prednisone. An extensive immunological work-up was negative, and no other infectious or autoimmune triggers were identified. The patient underwent a structured rehabilitation program with gradual improvement in motor function over the following weeks. Conclusions: This case illustrates a rare clinical scenario of pneumococcal myelitis associated with reactive arthritis in a patient without overt immunosuppression. It highlights the importance of considering bacterial etiologies in cases of acute transverse myelitis and the potential for unusual systemic immune responses such as reactive arthritis. Early recognition and the administration of appropriate antimicrobial and supportive therapies are crucial for improving neurological and systemic outcomes. To our knowledge, this is one of the first reported cases describing the co-occurrence of these two conditions in the context of S. pneumoniae infection.