Arnold Nerve Reflex: Vagus Nerve Mediation of Ear-Induced Cough
The cough response while cleaning the ear is mediated by the auricular branch of the vagus nerve, also known as Arnold's nerve, which innervates the external auditory meatus. 1
Anatomical Pathway
The Arnold nerve reflex operates through a specific vagal pathway:
Afferent nerves carried by the auricular branch of the vagus nerve (Arnold nerve) innervate the external auditory canal and can trigger cough when mechanically stimulated. 1
The cell bodies of these afferent neurons are located in the jugular (superior vagal) ganglia and terminate in multiple areas throughout the brainstem, including the nucleus of the solitary tract (nTS). 1
This reflex occurs in only a small subset of individuals (≤5% in the general population), making it a relatively uncommon phenomenon. 1
Clinical Significance and Prevalence
The prevalence of this reflex varies significantly between healthy individuals and those with chronic cough:
In healthy adults and children, Arnold nerve reflex occurs in only 2% of the population. 2, 3
However, in adults with chronic cough, the prevalence increases dramatically to 23-25.5%, representing a greater than 11-fold increase. 2, 3
The reflex is significantly more common in women (29-31.6%) than men (10.5-12.5%) among those with chronic cough. 2, 3
When present, the reflex is unilateral in approximately 88-90% of cases. 2, 3
Mechanism of Cough Induction
The cough triggered by ear stimulation involves central nervous system integration:
The cough initiated by ear stimulation likely involves integration of both ongoing airway vagal afferent nerve input and the additional afferent input arising from the ear canal. 1
The nociceptors that modulate cough have their cell bodies in the same jugular ganglia and terminate centrally in the same region of the nTS as Arnold's nerve, facilitating this reflex pathway. 1
Relationship to Cough Hypersensitivity Syndrome
The dramatically increased prevalence in chronic cough patients has important diagnostic implications:
The markedly elevated prevalence of Arnold nerve reflex in adults with chronic cough supports the concept of Cough Hypersensitivity Syndrome (CHS), where vagal hypersensitivity underlies chronic refractory cough. 2, 3, 4
Notably, children with chronic cough do not show increased prevalence of this reflex (3%, similar to healthy children at 2%), suggesting CHS is an acquired condition rather than congenital. 2, 3
Practical Clinical Considerations
When evaluating patients with unexplained chronic cough:
Examination of the external auditory canal should be performed, as foreign material (including hair) resting on the tympanic membrane or canal wall can trigger persistent cough through Arnold nerve stimulation. 5
Testing for Arnold nerve reflex involves gentle stimulation of the external auditory canal with a cotton-tipped applicator; cough occurring within 10 seconds is considered a positive response. 2, 3
In patients with refractory chronic cough and positive Arnold nerve reflex, treatment with gabapentin has been shown to successfully suppress both the cough and the reflex hypersensitivity, as this medication is effective for sensory vagal neuropathy. 4