Malignant Peripheral Nerve Sheath Tumors Without Muscle Weakness at Presentation: An Analysis of an Underappreciated Combination

Objective: Patients with malignant peripheral nerve sheath tumors (MPNSTs) of major motor nerves typically present with muscle weakness and pain. We aimed to analyze and characterize patients with MPNSTs of major motor nerves but without muscle weakness at initial presentation. Methods: We performed a retrospective search of MPNSTs in a major nerve evaluated and/or treated at our institution from 1994 to 2019. Patients with no muscle weakness and available magnetic resonance imaging were analyzed. Clinical materials and magnetic resonance imaging and positron emission tomography scans were reviewed for features of malignancy. This group of patients was compared with patients who presented with MPNSTs and muscle weakness. Results: Of 26 patients with MPNSTs who presented with no muscle weakness, 21 (81%) had a positive family history for malignancy. Only 16 (62%) magnetic resonance imaging scans were highly suspicious for malignancy. All 7 available positron emission tomography scans were highly suspicious for malignancy. Patients who presented with muscle weakness (n = 36) were more likely to have paresthesias and a history of neurofibromatosis 1 or radiation to the MPNST location (P < 0.05). Conclusions: MPNSTs of major motor nerves without muscle weakness represent an underappreciated subset of cases that have potential treatment and outcome implications. These patients presented with fewer symptoms and had fewer risk factors than patients with muscle weakness. Positron emission tomography should be considered as an additional method to try to anticipate the diagnosis of an MPNST.