Pathophysiology of iatrogenic and idiopathic vocal fold paralysis may be distinct

Abstract

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.

A comparative analysis of laryngeal nerve damage in patients with idiopathic vocal cord paralysis exhibiting different paralytic sides

“…Pei et al postulated that a significant number of instances of IVCP may be attributed to neuritis affecting the segment of vagus nerve situated proximal to the point at which the SLN branches off. 4 However, the absence of disparity between leftsided and right-sided paralysis in IVCP involving SLN aligns with the hypothesis posited by Mau et al 8 This hypothesis suggests that an equal number of patients with combined RLN and SLN involvement on both sides of IVCP implies a pathophysiological cause that occurs symmetrically and affects a location proximal to the bifurcation of RLN and SLN. 19…”

“…The involvement of SLN and CM in IVCP is a topic of interest. Mau's research revealed a significantly higher occurrence of simultaneous CM involvement in IVCP cases compared to iatrogenic cases 8 . Additionally, Chang et al's quantitative LEMG analysis demonstrated that 53% of IVCP patients exhibited concurrent deficits in the RLN and SLN.…”

“…Husain et al discovered that the duration of restored vocal function in cases of left‐sided IVCP exceeded that of right‐sided IVCP (179.8 vs. 111.3 days) 6 . In addition, the incidence of left vocal cord paralysis was higher among IVCP patients who did not regain their voice compared to those with right vocal cord paralysis (58.8% vs. 41.2%) 8 . Nevertheless, the extent of injury to the RLN and SLN in IVCP patients remains uncertain.…”

Patterns of Recurrence of Phonotraumatic Vocal Fold Lesions Suggest Distinct Mechanisms of Injury

“…Although certain vocal behaviors or vocal fold anatomic features may predispose to particular lesions, the actual development of these lesions and their recurrence are randomly determined processes aptly studied via stochastic models. Stochastic models have been previously applied in laryngology to elucidate the physiology of recovery from vocal fold paralysis, 20,21 and such an approach may offer novel insights into the genesis of phonotraumatic lesions.…”

Screening for Vocal Fold Movement Impairment in Children Undergoing Esophageal and Airway Surgery

“…The frequency of VFMI in patients without a prior at-risk operation is surprising at almost 1 in 5 patients (19%), and suggests a possible congenital etiology. 30,31 Given the prevalence of VFMI in our patient population and the poor discriminatory nature of relying on symptoms alone, we recommend a strategy of routine screening of all patients at risk, regardless of symptoms or prior surgical history.…”