Desmoid Fibromatosis in the Brachial Plexus Mimicking an Ulnar Nerve Entrapment

Introduction: Ulnar nerve entrapment is a common cause of sensory disturbance and weakness in the upper extremity, especially in patients with diabetes mellitus. However, if the symptoms are atypical and the patient has severe pain other differential diagnoses should be considered. Case report: A 37-year-old man with type 1 diabetes mellitus was referred to the hand surgery unit due to increasing pain, numbness and weakness in his right arm developing over more than one year. An ulnar nerve neurography was inconclusive and the patient had a frozen shoulder on the right side. Due to the pain, the patient required high doses of opioids. At examination, the clinical presentation did not correspond to an ulnar nerve entrapment why other causes were considered. A chest X-ray revealed a lesion in the apical part of the right lung. Consequtive CT scan, MRI and fine and core needle biopsies led to the diagnosis of a desmoid tumor. Surgery was deemed to be too mutilating and treatment was initiated with doxorubicin. Due to tumor and symptom progression the therapy was changed to PegIntron, then antiestrogen and NSAID and finally tyrosine kinase inhibitor (sorafenib) resulting in tumor shrinkage. Conclusion: Although nerve entrapment is a common cause of discomfort and impaired function in the upper extremities different etiologies, including various tumors, have to be considered when the symptoms are atypical and if the patient has severe pain. For these patients, the diagnostic work-up has to be broadened.