gms | German Medical Science

Objectives: Different hypotheses have been proposed for the pathophysiology of anterior and posterior interosseous nerve (AIN and PIN) palsy: compression, nerve inflammation or fascicular constriction. We hypothesized that critical reinterpretation of electrodiagnostic studies (EDX) and MRIs of patients with a diagnosis of AIN and PIN palsy could provide insight into the pathophysiology and treatment.

Method: A retrospective review was performed of all patients with a diagnosis of non-traumatic AIN and PIN palsy and an upper extremity EDX and MRI. The original EDX studies and MRIs were re-interpreted by a neuromuscular neurologist and musculoskeletal radiologist respectively, both blinded to our hypothesis.

Results: Sixteen patients met the inclusion criteria as having "isolated" AIN palsy. In all cases, reinterpretation of the MRIs demonstrated atrophy in at least one muscle not innervated by the AIN and did not reveal any evidence of compression of the AIN.

Fifteen patients met the inclusion criteria as having an "isolated" PIN palsy. Four cases (27%) had a defined mass compressing the PIN. The other 11 cases (73%) presented with at least one finding incompatible with the compression hypothesis.

Conclusion: All Patients in our series with presumed isolated, idiopathic AIN or PIN palsy had evidence of a more diffuse nerve - muscle involvement pattern, without any radiologic signs of nerve compression of the AIN or PIN itself. These data would favor an inflammatory pathophysiology, when a structural lesion compressing the nerve is ruled out with imaging.