In March 2015, a 73-year-old male with a history of HIV, well-controlled on antiretroviral therapy, presented with one month of left-side motor and sensory deficits. An MRI revealed a large, rim-enhancing brain lesion concerning for a tumor. Cerebrospinal fluid (CSF) showed no abnormalities, and a brain biopsy indicated tumefactive demyelination (TD). Treatment with IV methylprednisolone (IVMP) 1 g for 5 days followed by oral prednisone taper lead to improved. 

In April 2020, he experienced dizziness and worsening left-side weakness, along with a new cerebellar lesion. CSF showed one oligoclonal band, but other autoimmune markers were negative. Serum Anti-AQP4 IgG and Anti-MOG IgG were negative. IVMP followed by a oral taper and maintenance intravenous immunoglobulin (IVIG) led to recovery. In March 2021, a new brain lesion was discovered, and a week later, he developed progressive right arm and leg weakness and numbness, with an MRI showing a spinal lesion. Despite IVMP, his condition worsened, with an expanding spinal lesion. Plasma exchange and rituximab were started with good response. He has remained stable for over 2 years on rituximab and prednisone has been tapered to 10 mg daily. 

TD has been described on patients with HIV. This case presents unique aspects, namely well-controlled HIV for 2 years, late onset relapsing demyelinating disease, and distinct spinal lesion resembling neuromyelitis optica spectrum disorder (NMOSD). He required long-term immunosuppression with rituximab and prednisone. 

The case suggests that immune dysregulation related to HIV might contribute to this autoimmune disorder, resembling but distinct from multiple sclerosis (MS). The patient's age, tumefactive lesions, and LETM pattern set it apart from typical MS cases. 

This case adds significant insights into the neurologic complications of HIV and tumefactive demyelination (TD). Further research is essential to comprehend how immune dysregulation may trigger autoimmune conditions.