Definition: ECAC is the term used to encompass two entities, Tracheomalacia (TBM) and Excessive Dynamic Airway Collapse (EDAC). ECAC can be congenital or acquired.

Both conditions affect the collapsibility of the trachea and/or bronchi and result in reduced luminal diameter during expiration but have different pathogenesis and result in different tracheal morphology in exhale.

Traditionally TBM was defined as > 50% of reduction of the tracheal diameter between inspiration and expiration. This cut off is still applied for TBM diagnosis in the paediatric population, but recent research favours a cutoff of over 70%.

• In EDAC there is excessive inward bulging of the posterior membranous trachea during expiration with exaggerated luminal narrowing. The tracheal cartilage is normal.
• TBM is characterised by cartilaginous ‘malacia’ ie softening and weakening of the tracheal and/or bronchial cartilage. The resulting tracheal morphology differs depending on the aspect of the cartilage that has been affected, anterior, lateral or circumferential.

Risk factors and associations

• Chronic poorly controlled airways disease (COPD), particularly Asthma
• Raised BMI
• Sleep apnoea
• Steroid use has been debated as independent risk factor in patients with COPD.
• Inflammation (relapsing polychondritis, radiation therapy)
• Extrinsic compression
• Trauma, especially iatrogenic,  intubation

Symptoms

ECAC is infrequently suspected in patients presenting with dyspnoea as it does not manifest specific clinical symptoms. It is often asymptomatic and seldom causes symptoms on its own.The association and higher prevalence in patients with COPD are a confounding factor in underdiagnosis of this condition.  

Symptoms described in association with ECAC are:

• Barking cough
• Low pitched expiratory noises
• Recurrent infections
• Difficulty clearing phlegm