Which histologic findings are characteristic of pulmonary alveolar proteinosis (PAP)?

Updated: Dec 18, 2019
  • Author: Rodolfo Laucirica, MD; Chief Editor: Philip T Cagle, MD  more...
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Answer

The characteristic finding in tissue sections is the presence of eosinophilic granular material within the alveolar spaces. The overall lung architecture is preserved, and a mild chronic inflammatory infiltrate within the pulmonary interstitium may be present (see the images below).

Pathology of pulmonary alveolar proteinosis. Alveo Pathology of pulmonary alveolar proteinosis. Alveoli are filled with an eosinophilic granular material. Note the preservation of the normal lung architecture (hematoxylin and eosin, x200).
Pathology of pulmonary alveolar proteinosis. High Pathology of pulmonary alveolar proteinosis. High magnification illustrating the granular material and alveolar macrophages surrounded by intact alveolar septal tissue with minimal reaction (hematoxylin and eosin, x400).

This material is strongly periodic-acid-Shiff positive and diastase-resistant (DPAS) (see the image below).

Pathology of pulmonary alveolar proteinosis. Intra Pathology of pulmonary alveolar proteinosis. Intra-alveolar material is strongly periodic acid-Schiff (PAS) positive (diastase [D]-PAS, x200).

The diagnosis of PAP can also be established by cytologic evaluation of bronchoavleolar lavage (BAL) specimens.

Pathology of pulmonary alveolar proteinosis. Cytol Pathology of pulmonary alveolar proteinosis. Cytologic appearance of intra-alveolar granular material from a bronchoalveolar lavage sample (diastase-periodic acid-Schiff [DPAS], x400).

In addition, another finding reported in BAL samples from patients with PAP is the presence of dense globules that have well-defined borders (see the image below). [36, 37]

Pathology of pulmonary alveolar proteinosis. Bronc Pathology of pulmonary alveolar proteinosis. Bronchoalveolar lavage sample depicting dense globules with sharp borders seen in patients with pulmonary alveolar proteinosis (PAP) (Papanicolaou, x400).

Quantitative analysis of these globules has shown that the presence of 18 or more in BAL samples is a highly sensitive and specific marker for PAP. [38] These globules are believed to represent the multilaminated structures characteristic of PAP that are visible by electron microscopy. [37]


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