Pathophysiology of iatrogenic and idiopathic vocal fold paralysis may be distinct

Objective Spontaneous vocal recovery from idiopathic vocal fold paralysis (VFP) appears to differ in time course from recovery in iatrogenic VFP. This study aimed to determine if this difference could be explained by differing mechanisms causing recurrent laryngeal nerve (RLN) dysfunction, specifically whether idiopathic VFP is consistent with a focal RLN axonal lesion. Study Design Case series with mathematical modeling. Methods A review of 1267 cases of unilateral VFP over a 10-year period yielded 114 subjects (35 idiopathic, 79 iatrogenic) with a discrete onset of spontaneous vocal recovery. The time-to-recovery data were fit to a previously described two-phase model that incorporates the Seddon classification of neuropraxia and higher grades of axonal injury. Alternatively, the data were fit to a single phase model that does not assume a focal axonal lesion. Results Time to vocal recovery in iatrogenic VFP can be reliably modeled by the assumption of a focal axonal lesion, with an early recovery group corresponding to neuropraxia and a late recovery group with more severe nerve damage. Time to recovery in idiopathic VFP can be more simply modeled in a single phase, with a time course that mirrors those in diverse biological processes such as transcription and microtubule growth. Conclusion Idiopathic VFP may not be caused by a focal axonal lesion. Neuritis may be a compatible mechanism. The iatrogenic VFP data lend further support to the concept that the severity of RLN injury, not the length of axon to regenerate, is the chief determinant of recovery time after iatrogenic injury. Level of Evidence 4 Laryngoscope, 2019