Malignant peripheral nerve sheath tumor presenting with Pancoast syndrome in a patient with neurofibromatosis type 1

A 36-year-old woman with a history of neurofibromatosis type 1 (NF1) presented with acute onset of left-hand weakness, numbness, and pain. Neurological examination revealed Horner's syndrome, distal weakness in the C8-T1 myotomes, and sensory disturbances in the corresponding dermatomes. The constellation of these signs was consistent with Pancoast syndrome, involving both the sympathetic trunk and the lower brachial plexus. Nerve conduction studies demonstrated reduced distal compound muscle action potentials and reduced or absent sensory nerve action potentials from multiple nerves in the C8-T1 territories, supporting involvement of the lower trunk. Chest X-ray revealed a large apical mass, and cervical MRI showed that the mass was compressing the brachial plexus at that level, accounting for her symptoms. Histopathological examination of a specimen obtained from the apical mass confirmed malignant peripheral nerve sheath tumor (MPNST). The patient underwent multimodal treatment including partial resection, embolization, radiotherapy, and chemotherapy, which controlled tumor growth and allowed her to maintain functional independence over a two-year follow-up. This case highlights the importance of early recognition of MPNST in NF1 patients presenting with new neurological symptoms. It also underscores the value of careful neurological examination and electrophysiological studies in accurately localizing the responsible lesion.