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Pulmonary Alveolar Microlithiasis

Definition

  • Autosomal recessive lung disease characterized by filling of alveoli by calcospherites

Diagnostic Criteria

  • Clinical
    • Autosomal recessive
      • Caused by mutations in SLC34A2 sodium dependent phosphate transporter
        • Normally expressed by type II alveolar macrophages
    • Gradual onset and progression
    • About half of patients are found upon screening families of patients
      • Most are asymptomatic, even if the deposition is extensive
    • Average age of clinical presentation around 30
      • Can be found in infants
    • May take decades to progress to respiratory failure
    • No effective treatment except lung transplant
  • Radiology
    • Chest x-ray
      • “Sand storm” of calcified densities
      • Mainly lower and mid zones
    • High resolution computed tomography (HRCT)
      • Thickening and calcification of pleura, interlobular septa, bronchovascular bundles
      • Focal ground glass opacities and consolidation
      • Subpleural cysts
  • Histopathology
    • The diagnosis can usually be made without a biopsy based on history and radiology
      • Bronchoalveolar lavage and sputum may demonstrate microliths
    • Biopsy shows diffuse filling of alveolar air spaces by calcospherites
      • 250-750 microns but may reach 3 mm
      • Lamellated calcifications
      • Principally composed of calcium and phosphate
      • Late stages may show increased localization to subpleural, paraseptal and peri-bronchovascular regions
        • Fibrosis and ossification may occur in same areas

Gerald J Berry MD
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342

Original posting/updates: 11/20/10

Differential Diagnosis

Pulmonary Alveolar Microlithiasis Pulmonary Blue Bodies
Most are 250-750 microns Most are 15-40 microns
Most alveoli filled Usually few and scattered, alveoli not filled
Autosomal recessive Many cases associated with pneumoconiosis or interstitial lung disease

 

Pulmonary Alveolar Microlithiasis Pulmonary Corpora Amylacea
Calcified Not calcified
Most alveoli filled Usually scattered, alveoli not filled
Autosomal recessive, mean age of symptoms 30 years Increased numbers with aging, asymptomatic

 

Pulmonary Alveolar Microlithiasis Metastatic Calcification
Restricted to alveolar air spaces May involve air spaces, interstitium, bronchial walls
Spherical and laminated Irregular calcification
Autosomal recessive Associated with renal failure, parathyroid carcinoma

 

Pulmonary Alveolar Microlithiasis Heterotopic Ossification
Restricted to alveolar air spaces Interstitial
Spherical and laminated Lamellar spicules of bone
No cellular component Osteocytes in lacunae
Autosomal recessive Associated with prior inflammation

Classification / Lists

Idiopathic Interstitial Lung Diseases

Other Diffuse Parenchymal Lung Diseases

 

Bibliography

  • Travis WD, Colby TV, Koss MN, Rosado-de-Christenson ML, Müller NL, King TE Jr.  Non-neoplastic Disorders of the Lower Respiratory Tract, AFIP Atlas of Nontumor Pathology, First Series, Fascicle 2, 2002.
  • American Thoracic Society; European Respiratory Society. ATS/ERS International Multidisciplinary Consensus Classification of the Idiopathic Interstitial Pneumonias. This joint statement of the American Thoracic Society (ATS), and the European Respiratory Society (ERS) was adopted by the ATS board of directors, June 2001 and by the ERS Executive Committee, June 2001. Am J Respir Crit Care Med. 2002 Jan 15;165(2):277-304.
  • Visscher DW, Myers JL. Histologic spectrum of idiopathic interstitial pneumonias. Proc Am Thorac Soc. 2006 Jun;3(4):322-9.
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