Isolated spinal Rosai–Dorfman disease with secondary hypertrophic pachymeningitis: A case report with 20-year follow-up, highlighting rapid recurrence and <i>de novo</i> lesion formation

Background: Rosai-Dorfman disease (RDD) is a rare, benign histiocytic disorder that typically presents with cervical lymphadenopathy but may involve extranodal sites in up to 40% of cases. Isolated spinal RDD without systemic manifestations is exceedingly rare and often mimics more common neoplastic or inflammatory spinal pathologies. When associated with hypertrophic pachymeningitis (HP), the condition may demonstrate an aggressive and relapsing course, posing significant diagnostic and therapeutic challenges. Case Description: We report the case of a 41-year-old male who presented in 2005 with progressive paraparesis and voiding difficulty. Magnetic resonance imaging revealed an intradural extramedullary lesion compressing the cervical spinal cord from C5 to T1. Surgical resection was performed with a presumptive diagnosis of meningioma. Histopathology confirmed RDD with secondary HP. One month after surgery, the patient experienced early recurrence, which was managed with corticosteroids and azathioprine. Six years later, a de novo lesion developed at the thoracic level and responded to a short course of corticosteroid therapy. No further immunosuppressive treatment was required after 2015, and the lesion has remained stable without neurological symptoms. Serial imaging over 20 years demonstrated both regression and stability of the disease, illustrating its chronic, relapsing nature. Conclusion: This case represents one of the longest documented follow-ups of isolated spinal RDD with secondary HP. It highlights the potential for both early recurrence and delayed de novo lesion formation, even after apparent disease control. Surgical decompression remains essential for diagnosis and initial treatment, but long-term management may require tailored immunosuppressive strategies and sustained clinical and radiologic surveillance.