Neurofibromatosis type 1 (NF1) is a common tumor predisposition syndrome 
affecting approximately 1 in 4,000 persons. It is an autosomal-dominant disorder 
with half of the cases resulting from spontaneous mutations. This genetic defect 
leads to the formation of benign tumors or neurofibromas of the peripheral 
nervous system. Dermal neurofibromas may cause local discomfort and itching but 
are rarely associated with neurological deficit and do not undergo malignant 
change. The more extensive plexiform neurofibromas produce neurological 
complications in 27%-43% of patients with NF1 and may undergo malignant 
degeneration in 5% of cases. Patients with NF1 who develop pain or new 
neurological symptoms should have a rapid and thorough assessment for 
malignancy. In this report, we illustrate this point by presenting a patient who 
developed acute shoulder pain and weakness due to malignant degeneration of a 
plexiform neurofibroma involving the left brachial plexus, and review the 
literature on this subject.