Inducible laryngeal obstruction (ILO) describes a narrowing or inappropriate obstruction of the true vocal fold and/or the supraglottic structures in response to a trigger or stimulus. When this phenomenon occurs during exercise, it is referred to as exercise-induced laryngeal obstruction (EILO). The ILO terminology has been recently adopted. Since 2013, the term inducible laryngeal obstruction (ILO) has been used to describe “inducible laryngeal obstructions causing breathing problems. This was initially proposed by the European Respiratory Society, the European Laryngological Society, and the American College of Chest Physicians.” It replaces the older terms: vocal cord dysfunction (VCD) or paradoxical vocal fold motion (PVFM) that were widely used to describe the disease. In contrast to VCD and PVFM, the ILO terminology is more descriptive as it includes pathologies affecting the supraglottic structures and not only the vocal folds.
First observed in 1869 by Sir Morrell Mac-Kenzie, the condition was long thought to be psychogenic as later described in the New England Journal of Medicine. In the medical literature, many names have been used to describe the condition. Historically, Munchausen stridor, functional laryngeal obstruction, emotional laryngeal wheezing, irritable larynx syndrome, and factitious asthma, among other terms, were previously used to describe the disorder.
Over the years, multiple triggers have been reported associated with inducible laryngeal obstruction or VCD. This includes but is not limited to: odors, gastroesophageal reflux, exercise, irritants, and anxiety. Morris, in his review, further classifies the triggers in three main groups that encompass most previously reported triggers: psychogenic, irritant induced, and exertional. This activity will focus on exercise-induced laryngeal obstruction as it is frequently encountered in clinical practice.
Exercise-induced laryngeal obstruction is a common condition, especially among adolescents and young adults, with a prevalence reported to be between 5% to 10% based on limited studies. A recent study of 112 adolescents and young adults with EILO reports an onset of symptoms at 13.8 years and a mean age of diagnosis at 15.4 years. An earlier study reported age of 14.5 years. Most reports show that EILO is more common among female patients. One study describes a female to male odds ratio of 3.41. Another study showed that 91 of their 112 EILO patients (81.3%) were female. Typically, EILO tends to affect adolescent athletes with female predominance. It has also been described in those performing at a competitive level.
In healthy individuals, the vocal folds are usually abducted during inspiration. This is followed by slight adduction during expiration, thus allowing air movement to and out of the lungs.
In inducible laryngeal obstruction or PVFM, there is brief inappropriate adduction of the vocal folds during inspiration. This may manifest with audible inspiratory sounds. This phenomenon is exacerbated during exercise. Supraglottic obstruction can also happen. The term ILO is more inclusive of supraglottic structures as opposed to older definitions that are limited to the vocal fold or glottic structures. The exact cause and underlying mechanisms of EILO are not well described. Several hypotheses attempt to describe the pathophysiology. Airway size, as well as a history of congenital laryngomalacia, were thought to be associated with EILO. In 1999, Morrison et al. attributed the airway hyperresponsiveness in part to neuronal stimuli. Conditions like asthma and gastroesophageal reflux disease have also been commonly reported in the EILO population.
A broad range of symptoms has been reported in exercise-induced laryngeal obstruction. Dyspnea, stridor wheezing, dysphonia, throat tightness, chest tightness, and anxiety have all been reported. Dyspnea and stridor are the most common. Based on a review of 5 large series, 96.5% to 100% of patients had dyspnea, and 43% to 68% reported stridor. Patients cannot always identify stridor and often report “noisy breathing.” Symptoms are usually reported during exercise. In contrast to exercise-induced bronchospasm (EIB), which tends to occur after the completion of exercise, EILO symptoms are usually inspiratory, occur at peak exercise, and resolve within minutes. Response to bronchodilators is not typical. A detailed history is key, as some clues help achieve a diagnosis. Typical patients are female teenagers participating in sport, with no to minimal symptoms at rest. It is not uncommon to encounter patients who have undergone extensive evaluation or who have been treated extensively for EIB as EILO remains an underrecognized cause of exercise-induced dyspnea.
Physical examination is rarely helpful in diagnosing EILO as, by definition, symptoms occur during exercise and are not present at rest. The presence of wheezing or stridor at rest should prompt further evaluation to assess for other airway diseases.
The diagnosis of exercise-induced laryngeal obstruction can be made clinically if the presentation is typical, especially in the absence of other airway or breathing abnormalities.
Imaging has no role in the diagnosis of EILO, it helps rule out other respiratory and airway disorders when suspected.
Spirometry can be a helpful tool but is also non-diagnostic. Patients with EILO usually have normal flow volume loops on spirometry. Airflow obstruction, which is more characteristic of asthma, is not typical in EILO. Flattening of the inspiratory loop, suggestive of a variable extrathoracic obstruction, may occur in EILO.
Visualization of the larynx via flexible laryngoscopy during symptomatic periods remains the gold standard to diagnose EILO. The procedure is usually performed by trained otolaryngologists, pulmonologists, or speech therapists. This is more commonly done through exercise laryngoscopy. This technique consists of performing a transnasal flexible laryngoscopy after the subject is asked to exercise to peak in a diagnostic lab. Treadmills or stationary bicycles are typically used. The goal is to reproduce the symptoms that are otherwise absent at rest.
More recently, a new approach to laryngoscopy has been adopted. Continuous laryngoscopy during exercise (CLE), as opposed to exercise laryngoscopy, consists of continuous laryngoscopy throughout exercise on a treadmill or stationary bicycle. This test requires a set-up that is not always widely available to specialists. A flexible laryngoscope is attached to the head via a band or helmet, and the tip of the scope is introduced through the nose into the larynx. This allows visualizing the supraglottic and glottic structures in real-time throughout the exercise. During both techniques, cardiopulmonary data is collected as the patient exercises to peak in an attempt to reproduce EILO symptoms. EILO related findings on laryngoscopy include vocal cord narrowing, supraglottic narrowing, obstruction, and/or collapse of supraglottic structures.
Managing exercise-induced laryngeal obstruction requires a multidisciplinary approach. Typically, the team consists of otolaryngologists, pulmonologists, speech pathologists, and psychologists.
Referral to speech pathology for respiratory retraining therapy is considered first-line in managing EILO. Breathing techniques may vary; this is combined with behavioral therapy, reassurance, and teaching of respiratory mechanics, and sometimes biofeedback.
Bronchodilators or other inhaled therapies have no role in EILO management. These therapies can help if asthma coexists.
As discussed above, the main differential diagnosis is exercise-induced bronchospasm (EIB). EIB symptoms are usually expiratory, occur later during exercise, and respond to bronchodilators. Also, expiratory wheezing is more characteristic of EIB.
Chest tightness and dyspnea are also seen in some cardiac diseases as well as anxiety attacks.
Anatomical abnormalities of the larynx and trachea are also on the differential. This includes subglottic stenosis, laryngeal or tracheal compression due to a mass, tracheal ring or sling.
Overall, and based on the available literature, exercise-induced laryngeal obstruction is thought to be self-limited. The majority of patients respond to speech therapy. Refractory cases, especially when a supraglottic pathology is suspected, respond to supraglottoplasty.
Exercise-induced laryngeal obstruction (EILO) usually affects adolescents and young adults during exercise. It is due to a narrowing at the level of the upper airway and vocal cord that happens during inspiration (while trying to take a breath in). This can cause noisy breathing, shortness of breath, chest tightness, and cough.
The medical provider will likely want to rule out other conditions first like asthma, reflux, or upper airway issues.
If the diagnosis of EILO is confirmed, the patient should be referred to speech therapy to learn breathing techniques that will help prevent EILO.
The diagnosis of EILO can be missed or delayed. This is mainly due to receiving an alternative diagnosis like asthma that is more common then EILO, but also to the lack of awareness about this condition in the community. The delay or inappropriate diagnosis can result in patients receiving extensive workups and unnecessary medications.
This highlights the need to increase awareness about EILO in the community, especially primary care providers, school nurses, and sports coaches. Successful management of EILO requires a multidisciplinary approach. The team includes:
Pulmonologists are usually the first-line providers. Understanding the main difference between EILO and other differential is critical, especially asthma. It is also important for a pulmonologist to rule out other conditions.
Otolaryngologists have a central role in the evaluation of the upper airway structures. Also, in refractory cases, surgical management (supraglottoplasty) might be required.
Speech and language pathologists have a crucial role in managing EILO and preventing recurrent symptoms.
Psychology can also assist in behavioral therapy and biofeedback.
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