Nodular pulmonary amyloidosis is a subtype of pulmonary amyloidosis. It is considered a limited form of amyloidosis characterized by one or more pulmonary nodules or masses (amyloidomas).
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Epidemiology
Albeit rare in general, the nodular form is more common than the diffuse parenchymal form. The incidence is thought to peak around the 6th decade of life 5. There may be a slight male predilection 9.
Associations
Nodular pulmonary amyloidosis has been reported in Sjögren syndrome with lymphoid interstitial pneumonia 7.
Clinical presentation
Patients are usually asymptomatic. Patients rarely present with a cough or shortness of breath.
A tissue biopsy is deemed to be essential for a definitive diagnosis.
Pathology
It usually represents localized AL (immunoglobulin light chain) or AL/AH (mixed immunoglobulin light chain/heavy chain) amyloidosis although rare cases of systemic AL, localized AA, localized ATTRwt and localized Aβ2M/AL (mixed β2-microglobulin/immunoglobulin light chain) amyloidosis have been described 9.
There is nodular deposition of amyloid within the lungs. Amyloid is an inert, proteinaceous, homogeneous, acellular, and eosinophilic material.
Location
Nodular amyloid deposits usually appear in multiple sites; focal deposits are much less common.
Amyloid nodules are usually localized to the lower lobes and within the peripheral and subpleural regions.
Microscopic appearance
When subjected to histochemical staining with Congo red, it shows green birefringence under polarized light.
Radiographic features
CT
Four characteristic features have been described on CT 1,4,5:
sharp, smooth and lobulated contours
-
calcification
often central or in an irregular pattern within the nodule
seen in ~50% of cases
variable shapes and sizes: 0.5-15 cm
slow growth: often over the years and with no regression
Associated cavitation has been described but is very rare.
Masses may also be present in the trachea and bronchi, which can cause obstructive symptoms if sufficiently large 11.
Very rarely, lung cysts can also form (most often described with localized amyloidosis in association with Sjögren syndrome) 3,6,8.
Treatment and prognosis
Management options are dependent on the severity of symptoms whereas asymptomatic patients usually do not require treatment. In some situations, they are resected which can be both diagnostic and curative 5. Overall prognosis is considered good, compared to the diffuse parenchymal form 10.
Differential diagnosis
Nodular pulmonary amyloidosis is a great mimicker of various entities which include:
primary or metastatic malignant nodules
multiple pulmonary hamartomas 2
For a broader differential consider: