Radiology Quiz Case 3: Diagnosis

Diagnosis: Primary tracheal amyloidosis

Isolated tracheobronchial amyloidosis is an extremely rare entity, representing less than 1% of all cases of amyloidosis, with fewer than 150 cases reported in the literature.¹ The precise pathogenesis remains elusive, although the disease is hypothesized to be of plasma cell origin via overproduction and deposition of AL amyloid into tracheobronchial tissue.² Presenting symptoms are nonspecific, as in the present case, making the diagnosis more challenging. Three patterns of the disease have been described according to the location of the amyloid deposition: proximal, middle, and distal airway involvement, corresponding to the distal trachea, carina, and proximal mainstem bronchi, respectively.¹ A fourth “diffuse” pattern has also been reported, with amyloid involvement in all 3 areas.³ The pattern of amyloid deposition has been shown to be predictive of the presenting symptoms. Proximal disease is associated with generalized signs of upper airway obstruction such as stridor and hoarseness. Middle and lower airway variants may present with chronic cough, hemoptysis, repeated pneumonia, or asthmalike symptoms.^{1 ,4} There appears to be little to no association between tracheobronchial and systemic amyloidosis. In the largest series with long-term follow-up, O’Regan et al¹ found that none of the cases that presented with primary tracheobronshial amyloidosis progressed to systemic amyloidosis, nor did tracheobronchial amyloidosis develop in cases that presented with systemic amyloidosis over the 15-year duration of their study.

Bronchoscopy with biopsy is the criterion standard for diagnosis of tracheobronchial amyloidosis; however, a characteristic imaging pattern has been observed in some cases. Some authors have described airway narrowing and mural thickening together with mural calcifications sparing the posterior tracheal membrane as highly suggestive of tracheobronchial amyloidosis.¹ Mural calcifications were not observed in our case, and because of the extreme rarity of the disease, the exact prevalence of these findings in tracheobronchial amyloidosis remains unclear.

Management, as well as prognosis, often relates to the site of primary amyloid involvement. Proximal involvement, as in our case, portends the worst prognosis, with up to 30% mortality from progression of disease at 7 to 12 years in one series.¹ Amyloidosis isolated to the middle and/or distal airways in the same series tended to follow a more indolent course. Isolated upper or middle tracheal lesions may be considered for segmental tracheal resection or open debulking via laryngofissure after careful tracheoscopic evaluation, although concerns for local recurrence or anastomotic compromise owing to local amyloid deposition has led to endoscopic management and radiation therapy emerging as preferred treatment options.^{5 - 6} Endoscopic management often relies on serial bronchoscopy with debulking of intraluminal lesions using traditional laryngeal/bronchial forceps, microdebriders, balloon dilatation, and lasers, with or without stenting of the airway. Multiple debridements are often required given the progressive nature of the disease, although optimal timing of these interventions remains to be determined. Tracheostomy may be required in severe cases and portends a grim prognosis, with a 60% mortality rate.¹

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