MEDizzy - A 45-year-old man presents with shortness of breath, cough

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Respiratory System

A 45-year-old man presents with shortness of breath, cough with mucoid sputum, and some weight loss, and has diffuse, bilateral alveolar infiltrates on chest x-ray. Pulmonary function tests reveal decreased diffusing capacity and hypoxia. A lung biopsy reveals intensely eosinophilic granular material within alveoli. Workup finds the presence of anti-GMCSF antibodies in his serum. What is the best diagnosis?

ExplanationPulmonary alveolar proteinosis (PAP) is a rare disease that is characterized histologically by the accumulation of intensely eosinophilic, proteinaceous, granular substance in the intra-alveolar and bronchiolar spaces. The alveolar walls are relatively normal, without inflammatory exudate or fibrosis, although type II pneumocytes may be hyperplastic. The process is often patchy, with groups of normal alveoli alternating with groups of affected alveoli. Acicular (cholesterol) clefts and densely eosinophilic bodies (necrotic cells) are found within the granular material. Distinction from edema fluid may be difficult, but PAP alveolar material stains with periodic acid–Schiff (PAS). There are three distinct clinical classes of this disease: acquired, congenital, and secondary PAP. Currently it is postulated that acquired PAP is associated with the development of anti-GM-CSF antibodies. Congenital PAP is quite rare and is associated with mutations of genes coding for either surfactant protein B, GM-CSF, and GM receptor β chain. Secondary PAP is associated with occupational exposure to silica or aluminum dusts. It also occurs in immunosuppressed patients and toxic drug reactions and is often associated with infections by organisms such as nocardia, fungi, and TB (possible impaired macrophage killing). The treatment of choice is bronchoalveolar lavage to remove the proteinaceous debris.