Arnold’s nerve ear-cough reflex:
In the Arnold’s nerve ear cough reflex, the cough is induced by mechanical stimulation of the external auditory canal by the auricular branch of the vagus nerve (Arnold nerve). The test is performed with a cotton swab on a stick by stimulating the ear by inserting the swab 3 to 5 mm into the external auditory canal and rotating it for 2 to 3 seconds. The test is considered positive if the patient coughs within 10 seconds. The test should be performed on both sides, as many people have only one side affected. The test is positive in 2% of healthy children and adults, and in 3% of children and 25% of adults with a chronic cough. A positive reflex is more common in women than in men and is unilateral in over 90% of patients (47). Interestingly, hair in the ear canal can stimulate Arnold’s nerve and trigger the cough reflex (oto-tricho-tussia). Such patients can be treated by simply removing the hair (48). This can be applied to any foreign body or earwax impaction in the ear canal. Therefore, examination of the external auditory canal should be routine in patients with chronic cough, especially in the elderly (49).
The high prevalence of positive Arnold nerve reflex in patients with chronic cough suggests that chronic cough is a neuropathic condition that may be secondary to sensory nerve damage. It is usually accompanied by other neuropathic features, such as throat irritation (laryngeal paresthesia). The cough is triggered by non-tussive triggers such as cold air and food (referred to as allotussia or urge-to-cough). The low prevalence of the positive reflex in children with chronic cough (3%) compared with adults (25%) suggests that the hypersensitivity of this reflex may have been acquired by viral infections (50).
Holmes-Adie syndrome is another rare cause of chronic cough; it is due to autonomic dysfunction involving the vagus nerve. Autonomic dysfunction is a common feature of this disorder; it is attributed to lesions of both afferent and efferent sympathetic and parasympathetic neurons. Airway reflux secondary to vagal dysfunction is a possible etiology of cough in these patients. Patients present with anisocoria, abnormal deep tendon reflexes, patchy areas of hyperhidrosis or anhidrosis, and chronic cough (51). Many patients with sensory neuropathic cough have been relieved by neuralgia Neuromodulator medications can help reduce or eliminate the cough by decreasing the ”misfiring” of nerves caused by sensory neuropathic cough (52).