Fact-sheet: Alveolar proteinosis


Updated on 09/17/2021 at 12:16 PM

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Definition

Disease related to the accumulation of amorphous phospholipoproteinaceous material within the distal air spaces of the lung (alveolar filling) due to impaired macrophage clearance of intra-alveolar surfactant.
Rare diffuse infiltrative lung disease.
6 cases/1,000,000 inhabitants.
Male predominance: ratio 2.5/1.
Three forms:
- Acquired or primary PAP (90%)
- Congenital PAP
- Secondary PAP
In primary forms: no exposure factor identified, but the bronchoalveolar fluid contains antibodies directed against GM-CSF (Granulocyte macrophage colony stimulating factor).
In secondary forms: 2 responsible genetic mutations
- deletion mutation leading to an unstable mRNA and surfactant protein B
deficiency
- mutation of the beta chain of the GM-CSF receptor
In secondary forms, two types:
- non-exogenous forms: following organ transplantation or a chronic condition (chronic myeloid leukemia, lymphocytic leukemia, myelodysplastic syndrome, AIDS) with absence of expression of the beta chain of the GM-CSF receptor
- exogenous forms or forms related to occupational exposure: silica, cement, petroleum, paint, wheat flour: surfactant accumulation in the alveoli due to engorgement of macrophages by exogenous substances

Clinical features

Clinical examination may be normal
Dyspnea
Non-productive cough +/- expectoration of gelatinous material
General malaise, low-grade fever
PFTs: restrictive pattern, decreased DLCO

Laboratory findings

Bronchoscopy + BAL: milky white fluid with abundant granular, acellular, eosinophilic, lipoproteinaceous material
Anti-GM-CSF antibodies: 100% of primary forms, Se/Sp>95%

Radiography

Alveolar pattern with complete acinar filling and intense opacification of non-segmental territories potentially involving both lung fields and even resulting in a white lung in severe forms with progression to ARDS

CT

CRAZY PAVING: ground-glass opacities + intra- and inter-lobular septal thickening

Management

Treatment:
- Repeated whole-lung lavage under general anesthesia
- Inhaled GM-CSF +/- associated subcutaneous route
- Transplantation

Differential diagnosis

Little doubt in its typical form, but:
- Alveolar hemorrhage
- Cardiogenic pulmonary edema
- ARDS
- Bronchioloalveolar carcinoma