We report a 52-year-old woman with progressive limb numbness and weakness for 9 months. Cerebrospinal MRI revealed longitudinally intramedullary myelopathy, accompanied by involvement of brainstem and cranial nerve roots. The spinal cord lesions were hyperintense on T2-weighted imaging (T2WI) with several round-like hypointense foci that showed nodular or circular enhancement, a feature known as the “flip-flop sign”. Given the chronic progressive course and characteristic imaging findings, differential diagnoses including neoplastic, infectious, inflammatory or autoimmune etiologies were considered. Despite an unremarkable cerebrospinal fluid (CSF) examination with nonspecific markers of inflammation, whole-body PET-CT revealed multiple hypermetabolic lymph nodes in the neck, prompting lymph node biopsies. Histopathological and immunostaining analysis of the lymph nodes established the diagnosis of neurosarcoidosis, thus sparing the patient from having a spinal cord biopsy. After immunotherapy, her neurological function improved significantly within 2 months. This report offers a framework for the evaluation, diagnosis, and management of patients with neurosarcoidosis with subacute or chronic spinal cord involvement presenting with the “flip-flop sign”.