title: Nontraumatic "isolated" posterior interosseous nerve palsy: Reinterpretation of electrodiagnostic studies and MRIs.
abstract: BACKGROUND
  Different hypotheses have been proposed for the pathophysiology of posterior interosseous nerve (PIN) palsy, namely compression, nerve inflammation, and fascicular constriction. We hypothesized that critical reinterpretation of electrodiagnostic (EDX) studies and MRIs of patients with a diagnosis of PIN palsy could provide insight into the pathophysiology and treatment.
  
  
  METHODS
  We retrospectively reviewed patients with a diagnosis of nontraumatic PIN palsy and an upper extremity EDX and MRI. The original EDX studies and MRIs were reinterpreted by a neuromuscular neurologist and musculoskeletal radiologist, respectively, both blinded to our hypothesis.
  
  
  RESULTS
  Fifteen patients met the inclusion criteria, i.e., having an "isolated" PIN palsy. Four patients (27%) had a defined mass compressing the PIN. The remaining 11 patients (73%) presented with at least one finding incompatible with the compression hypothesis: physical examination revealed that weakness in muscles was not innervated by the PIN in 4 patients (36%); EDX abnormalities not related to the PIN were found in 4 patients (36%); and reinterpretation of the MRIs showed muscle atrophy or nerve enlargement beyond the territory of the PIN in 9 patients (82%), without any evidence of compression of the PIN in the proximal forearm.
  
  
  CONCLUSIONS
  The eleven patients in our series with presumed isolated and idiopathic PIN palsy had evidence of a more diffuse nerve-muscle involvement pattern, without any radiologic signs of nerve compression of the PIN itself. These data would favor an inflammatory pathophysiology when a structural lesion compressing the nerve is ruled out with imaging.
authors.affiliation: Mayo Clinic, Department of Neurologic Surgery, 200 1st Street South West, Rochester, MN 55905, USA.
authors.forename: Andrés A
authors.initials: AA
authors.lastname: Maldonado
authors.affiliation: Mayo Clinic, Department of Radiology, 200 1st Street South West, Rochester, MN 55905, USA.
authors.forename: Kimberly K
authors.initials: KK
authors.lastname: Amrami
authors.affiliation: Mayo Clinic, Department of Neurology, 200 1st Street South West, Rochester, MN 55905, USA.
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Mauermann
authors.affiliation: Mayo Clinic, Department of Neurologic Surgery, 200 1st Street South West, Rochester, MN 55905, USA. Electronic address: spinner.robert@mayo.edu.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Spinner
mesh_terms: D000328:Adult; D000368:Aged; D004568:Electrodiagnosis / Q000379:methods*; D005260:Female; D005500:Follow-Up Studies; D005542:Forearm / Q000294:innervation*; D005544:Forecasting; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009443:Neuritis / Q000150:complications* / Q000175:diagnosis / Q000503:physiopathology; D010243:Paralysis / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology; D012189:Retrospective Studies
keywords: Brachial plexus neuritis; Fascicular constriction; Nerve compression; Neuralgic amyotrophy; Parsonage–Turner syndrome; Posterior interosseous nerve palsy