Consider Cough as a Possible Neurological Sign

Because cough reflex sensitivity could increase or decrease in many neurological disorders, clinicians should consider this possibility when patients present with coughing, according to an article recently published in the World Journal of Critical Care Medicine.

Cough is a common complaint for patients seeking medical advice. Although it is often assumed to be a sign of respiratory issues, it could also be a crucial neurological sign and should be considered carefully.

There are 3 main types of coughs: Reflex cough (type 1), voluntary cough (type 2), and evoked cough (type 3), which follows the urge to cough. Both reflex and voluntary cough initiate similar mechanisms of cough motor behavior.

Coughing is a reflex predominantly mediated by control centers in respiratory areas of the brainstem, which is modulated by the cerebral cortex. Therefore, cough reflex sensitivity can be increased or decreased by various neurological disorders.

Cough without an apparent medical etiology is refractory to medical management, which could suggest a possible psychiatric or psychological basis. Although previously called psychogenic, habit, or tic cough, this is now called somatic cough.

To diagnose the cough as a tic, clinicians rely on core tic criteria, such as suppressibility, distractibility, suggestibility, variability, presence of a premonitory sensation, and whether the cough is single or part of many tics. Behavior therapy, psychotherapy, deep brain stimulation, botulinum injections, antiepileptics, and antidepressants are possible therapeutic options.

Neuromyelitis optica spectrum disorder (NMOSD), cerebellar disorders, and vagal neuropathy could offer alternative causes for cough. NMOSD is a rare autoimmune disease of the central nervous system with inflammation of the long segments of the spinal cord inflammation and optic nerve with attacks of intractable vomiting and hiccoughs due to autoimmune-mediated lesion. This cough is caused by autonomic dysregulation secondary to loss of parasympathetic innervation.

In cerebellar disorders, the neurons in the ventrolateral medulla that create cough and respiratory patterns interact with neural networks in the cerebellum-rostral interposed nucleus, rostral fastigial nucleus, and infra-cerebellar nucleus. The cerebellar nuclei are involved in neural activities necessary for breathing and coughing, which can cause a significant reduction in cough frequency after cerebellectomy or with interposed nucleus lesion.

The prevalence of chronic cough in vagal neuropathy varies based on the underlying pathology. It is prevalent with laryngeal disorders, such as laryngeal sensory neuropathy, post-viral vagal neuropathy, and irritable larynx. However, it is rare with hereditary sensory neuropathy and vitamin B12 deficiency.

Vagus nerve dysfunction can be seen after viral infections, irritant exposure, or complicated chronic conditions, such as asthma. Behavioral therapy and medical management are needed to treat the hypersensitive cough reflex.

Other neurological conditions that affect the peripheral and central nervous systems can result in diminished cough reflex sensitivity. Diminishing cough reflex is associated with a high risk of developing pneumonia and increased morbidity and mortality rates in these diseases. Examples of conditions that can decrease the reflex include brain hypoxia and cerebrovascular events; motor neuron diseases; neuromuscular diseases; and peripheral neuropathy.

Various cough reflex tests can be performed to help diagnose neurologic disorders. Arnold’s nerve ear-cough reflex triggers the cough using mechanical stimulation of the external auditory meatus through the auricular branch of the vagus nerve. Alternatively, other signs of potential neurologic disorders include cough syncope and cough headache.

REFERENCE

Al-Biltagi M, Bediwy AS, Saeed NK. Cough as a neurological sign: What a clinician should know. World J Crit Care Med. 2022 May 9; 11(3): 115-128. doi:10.5492/wjccm.v11.i3.115