Cough
A cough is an acute expulsion of air from the large air passages that serve to clear them of foreign particles fluids irritants and microbes. Coughing can be habitual as a protective reflex with three stages of the cough reflex, namely an inhalation forced expiration against a closed glottis and a violent expulsion of air from the lungs after opening the glottis commonly with a characteristic sound. Repeated coughing generally signifies the existence of a disease.
Cough is a universal respiratory symptom leading patients to seek professional consultation. Apart from being an essential respiratory sign, it also serves as an important neurological sign. There are three fundamental types of coughs: Reflex cough type I, voluntary cough type II, and evoked cough type III. Cough is a reflex with predominant mediation by control centers of the respiratory regions of the brainstem that is modulated by the cerebral cortex.
Increased cough reflex sensitivity might occur in various neurological disorders including brainstem space occupying lesions Chiari type I malformations secondary medullary lesions tics conditions like Tourettes syndrome somatic cough cerebellar neurodegenerative disease and allergic and non allergic chronic vagal neuropathy. In contrast cough sensitivity is reduced in multiple sclerosis brain hypoxia, cerebral hemispheric stroke with a brainstem shock, Parkinsons disease dementia caused by Lewy body disease, amyotrophic lateral sclerosis, and peripheral neuropathy as diabetic neuropathy, hereditary sensory and autonomic neuropathy type IV, vitamin B12, and folate deficiency.
Causes of cough
Arnold’s nerve ear-cough reflex, syncopal cough, cough headache, opioids-associated cough, and cough-anal reflex are symptoms that may diagnose underlying neurological disorders. Cough reflex testing is a rapid, simple, and inexpensive test done on examination of the cranial nerves. In this article, we have discussed the place of cough in different neurological diseases that either augment or diminish sensitivity to cough.
Treatment must aim at the aetiology , giving up smoking or stopping ACE inhibitors. Cough suppressants codeine or dextromethorphan are often used but are contraindicated in children. Alternative treatments may work on airway inflammation or increase mucus expectation. Since cough is a reflexive protective event, suppressing cough may have destructive consequences, particularly if the cough is productive giving phlegm.
A knowledge of the anatomic physiologic and pathophysiologic mechanisms of cough is required to diagnose and manage patients with cough appropriately. In most individuals acute and self limiting cough is typically secondary to a viral upper respiratory infection; chronic and persistent cough is typically secondary to chronic bronchitis or postnasal drip.
In the rest of the individuals, to identify the etiology of cough, one needs to methodically review anatomic sites in which receptors and afferent nervous tracts are found. The treatment of cough is definitive in the sense that it relies on identifying its exact etiology and then starting specific therapy for the underlying disorder. Only if the etiology of cough is still not identified or if cough serves no beneficial function and its complications pose a possible risk to the patient, should symptomatic therapy be employed. Combination cough medicines must not be used.
Chronic cough
It is a ubiquitous symptom that poses a formidable challenge to clinicians because relief is not always forthcoming despite treatment of the underlying cause, an apparent cause may be unobtainable, and existing antitussives have reasonably poor efficacy and unacceptable side-effects. Chronic cough patients usually complain of a variety of sensory symptoms that are consistent with upper-airway and laryngeal neural dysfunction. In addition, cough induced by minimal physical and chemical stimuli is also reported by the patients, pointing towards cough-reflex hyperresponsiveness.
The pathophysiological mechanisms for the peripheral and central augmentation of afferent pathways of cough have been found to exist, and strong evidence exists for neuropathy of vagal sensory nerves following upper-respiratory viral illness or inhalational exposure to allergic and non-allergic irritants. Here we put forward the case that chronic cough is a neuropathic disease resulting from nerve damage as a consequence of inflammatory, infective, and allergic processes. Supporting this contention, we review data on the efficacy of treating chronic cough with medications employed in treatment of neuropathic pain, including gabapentin and amitriptyline. Classifying cough as a neuropathic disorder might give rise to novel, more potent antitussives.
Cerebral disorders
Urgento-cough is a thought sensation that is required to trigger and suppress the reflex cough stimuli below the normal amount to produce a motor cough. Cough is controlled by cerebral cortical or subcortical areas and also involves activation of several brain areas including the insula, anterior midcingulate cortex, primary sensory cortex, orbitofrontal cortex, supplementary motor area, and cerebellum.
Cough, without a seemingly medical etiology, is resistant to medical treatment, underlying a potential psychiatric or psychological origin was once referred to as psychogenic, habit, or tic cough. Today, the term psychogenic is substituted with somatic cough, and the term habit was substituted with tic cough, as per the Diagnostic and Statistical Manual of Mental Disorders fifth. The prevalence of somatic cough syndrome is not well established owing to limited and inconsistent studies. It, however, occurs in approximately 3% to 10% of children with chronic cough of indeterminate cause and in approximately 3.02% of Chinese in-patients with chronic cough.
The discrimination between somatic and non-somatic chronic cough is sometimes difficult since chronic cough patients are also susceptible to psychomorbidities like depression and anxiety, which may induce a chronic cough. Somatic cough syndrome can be diagnosed only when the patient fulfills the DSM-5 criteria regardless of the absence or presence of the nocturnal cough or cough with honking quality. Certain groups of patients with somatic cough disorders can be helped by non pharmacologic attempts at hypnosis or suggestion therapy or combinations of reassurance counseling or referral to a psychologist or psychiatrist.
Tic cough
Tic cough is a type of vocal or phonic tics that are sudden brief intermittent involuntary or semi voluntary cough. It can be accompanied by other motor or vocal tics like throat clearing sniffing grunting squeaking screaming, barking blowing and sucking noises.
In diagnosing the cough as a tic we rely on fundamental tic criteria like suppressibility distractibility suggestibility variability occurrence of a premonitory sensation and whether the cough is solitary or part of numerous tics. Tourettes syndrome is a classic neuropsychiatric condition presenting with involuntary motor and phonic tics that include coughing, grunting, and wheezing. Phonic tics may be mistaken for respiratory tract diseases like asthma and infections of the upper and lower respiratory system. Tourettes syndrome is diagnosed with proper history and detailed neurological examination.
Treatment of cough
There is little evidence on how effective nonmedicinal therapies are. From a physiological perspective it makes sense to drink enough fluid, but to consume too much may carry the risk of hyponatremia. Avoidance of smoking is advised, since active and passive smokers recover from a cold more slowly. The evidence from RCTs is conflicting regarding the effectiveness of nasal sprays/rinses with saline solution or inhaling steam. Coughing into the elbow and not the hand is the best way to prevent transmission. Washing the hands frequently during periods of the year when common colds are more common is a rational prophylactic practice.
Cough with a cold or acute bronchitis/sinusitis usually subsides with no specific drug treatment. The patient should be informed that the disease is self-limiting and benign and hence no drugs are to be administered. Drugs to suppress the symptoms can be given, however, if the patient desires so.
Analgesics like acetaminophen and ibuprofen can be advised for symptomatic relief of headache and muscle pain. RCTs have demonstrated no benefit of antitussives compared to placebo for suppressing the desire to cough in the common cold. However, they might help sleep at night. Expectorants are also prescribed to productive cough patients despite the absence of evidence supporting their effectiveness for the treatment of acute cough no high-quality observational studies or RCTs are available for this indication. Whether results from studies on chronic bronchitis can be generalized to acute bronchitis or the common cold is unclear. Decongestant nasal sprays or drops relieve symptoms temporarily, but for more than 7 days gives no lasting relief and may result in atrophic rhinitis