A 67-year-old male with known Parkinson’s disease presented elsewhere in September 2023 with progressive neck and occipital pain. Imaging with MRI and FDG-PET revealed an expansile, lytic, hypermetabolic lesion involving the C2 vertebral body with pre- and paravertebral soft tissue extension causing mild spinal cord compression. The patient underwent posterior decompression, subtotal tumor excision, and stabilization with C1–C4 fixation in December 2023. Histopathology and immunohistochemistry confirmed a diagnosis of plasmacytoma. Despite surgical advice, the patient did not complete adjuvant radiotherapy. Eight months later, he developed sudden severe neck pain following a trivial sneeze. Repeat PET-CT demonstrated marked disease progression with increased metabolic activity at C2, new rib lesions suggestive of systemic spread, and extensive intradural and extradural extension encasing the cervical cord and vertebral artery. Bone marrow biopsy showed normocellular marrow with 3% plasma cells. Palliative radiotherapy (20 Gy in five fractions) was administered, followed by systemic chemotherapy with bortezomib, lenalidomide, and dexamethasone. The patient subsequently presented to our emergency department with profound cervical mechanical instability, unable to support his head. Multidisciplinary consensus recommended definitive surgical stabilization due to the high risk of catastrophic failure and neurological compromise. Preoperative CT angiography with three-dimensional reconstruction was performed to delineate vertebral artery anatomy. A posterior extended occipitocervical fusion using a double-rod construct and structural bone grafting over morselized graft was undertaken to restore stability. Postoperatively, the patient demonstrated improved head control and pain relief. He later required flap reconstruction for wound coverage and continues on oncologic surveillance and systemic therapy. This case shows the aggressive and destabilizing nature of upper cervical plasmacytoma, the consequences of incomplete adjuvant therapy, and the importance of early multidisciplinary intervention. Extended occipitocervical stabilization in such cases with severe biomechanical compromise, provides pain relief, spinal stability, and improved quality of life.