Pulmonary Alveolar Microlithiasis

Epidemiology

Incidence: rare disorder
Familial Clustering: present in >50% of cases
- Especially clusters in siblings
Age: most cases are diagnosed in 20’s-40’s
- Has been reported in all age groups though
Sex
- Female>male in familial cases
- Female=male in sporadic cases

Accumulation of hydroxyapatite (calcium and phosphorous) crystal concretions (0.01-3 mm) in alveolar spaces (probably due to some inborn error of caclium metabolism)
Over time, alveolar walls become fibrotic

CXR/Chest CT Pattern
- Early: characteristic diffuse bilateral calcific alveolar infiltrates (with air bronchograms) with lower lobe predominance
  - “Vanishing heart phenomena”: due to microliths adjacent to heart border
  - “Black and white” pleural-related lines (pathognomonic): white thick line at subpleural area adjacent to black pleural line (a Mach band)
  - Chest CT: lower lobe and subpleural predominance of intra-alveolar calcified nodules, pleural calcifications may be seen
- Later: ILD, evidence of pulmonary hypertension
PFT’s: usually normal until late in course, when restriction with decreased DLCO occurs
FOB: TBB may aid in confirming diagnosis
Bone Scan: may aid in confirming diagnosis
Serum Calcium and Phosphorous: normal
CBC: polycythemia (occurs late in course, associated with hypoxemia)

(may be asymptomatic even with extensive CXR abnormalities)

Interstitial Lung Disease (see [[ILD-Etiology]])
- Clubbing
- Cough and dyspnea: occur late in course
- Expectorated Microliths: occurs infrequently
- Crackles: occur with later development of ILD
Cor Pulmonale (see [[Pulmonary HTN-Etiology]])