|LETTER TO EDITOR
|Year : 2019 | Volume
| Issue : 1 | Page : 45-46
An Unusual Cause of Miliary Shadows—Pulmonary Alveolar Microlithiasis
Govindaraj Vishnukanth1, Bheemanathi H Srinivas2, Pavirala Saitej3, Archana Mallick4
1 Associate Professor, Department of Pulmonary Medicine, Jawaharlal Institute of Postgraduate Medical Education and Research(JIPMER), D nagar, Puducherry, India
2 Associate Professor, Department of Pathology, Jawaharlal Institute of Postgraduate Medical Education and Research(JIPMER), D nagar, Puducherry, India
3 Junior Resident, Department of Pulmonary Medicine, Jawaharlal Institute of Postgraduate Medical Education and Research(JIPMER), D nagar, Puducherry, India
4 Senior Resident, Department of Pulmonary Medicine, Jawaharlal Institute of Postgraduate Medical Education and Research(JIPMER), D nagar, Puducherry, India
|Date of Web Publication||18-Jan-2019|
Department of Pulmonary Medicine, Jawaharlal Institute of Postgraduate Medical Education and Research (JIPMER), D nagar, Puducherry, 605006
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Vishnukanth G, Srinivas BH, Saitej P, Mallick A. An Unusual Cause of Miliary Shadows—Pulmonary Alveolar Microlithiasis. J Assoc Chest Physicians 2019;7:45-6
|How to cite this URL:|
Vishnukanth G, Srinivas BH, Saitej P, Mallick A. An Unusual Cause of Miliary Shadows—Pulmonary Alveolar Microlithiasis. J Assoc Chest Physicians [serial online] 2019 [cited 2019 Dec 10];7:45-6. Available from: http://www.jacpjournal.org/text.asp?2019/7/1/45/250467
All that glitters is not gold. Similarly, not all miliary opacities on chest x-ray are tuberculosis. Pulmonary alveolar microlithiasis (PAM) is a rare congenital disorder that can mimic miliary tuberculosis radiologically. A 47-year-old chef presented with complaints of progressively worsening dyspnea of 6 months duration. Chest x-ray had diffuse nodular opacities involving all the zones with radio density comparable to that of bone. There was also silhouette of diaphragm and heart borders. Possibilities of acute respiratory distress syndrome (ARDS), H1N1 pneumonia, military tuberculosis, and PAM were considered. Computed tomography (CT) of chest showed bilateral interlobular and intralobular septal thickening with bilateral calcifications in the middle and lower lobes [[Figure 1]a]. Percutaneous lung biopsy showed dilated alveoli filled with basophilic concentric material (calcification) without any granuloma or malignant cells, thereby confirming our diagnosis of PAM [[Figure 1]b].
|Figure 1 (a) CT of chest (lung window) showing bilateral interlobular and intralobular septal thickening with bilateral calcifications in the middle and lower lobes. (b) Histopathology specimen of percutaneous lung biopsy shows dilated alveoli filled with basophilic concentric calcifications (H&E ×200)|
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PAM is a rare entity with unknown etiology and pathogenesis. PAM is characterized by the presence of a high concentration of microliths or calcispherites in the lung alveolar spaces. In India, only about 30 cases have been reported from different regions., Of the multiple theories regarding etiology of PAM, the most accepted theory is that of a congenital error of the enzyme carbonic anhydrase. Mutation of SLC34A2 gene is also implicated causing formation of calcium phosphate–rich microliths.
PAM is usually diagnosed at a late stage. Majority of the patients are asymptomatic at the time of diagnosis. PAM can be suspected radiologically. PAM is a noticeable example of clinical and radiological dissociation. On chest radiograph, typical occurrence of fine sand-like calcific micronodulation is evident (also referred to as sandstorm lung). Felson described the presence of a linear radiolucency in the lateral pleura of lung on chest radiographs of PAM and named it as a black pleural line.
The radiological lesions are well made out with CT of the chest. On CT, a characteristic abnormal calcification of the interlobular septa, bronchovascular bundles, and pleura can be seen. These calcifications are symmetrical and are more predominant along the borders of the heart and in the posteroinferior portions of the lung.
Although a clinical picture with radiological appearance is sufficient to make a diagnosis of PAM, sometimes a pathological confirmation is needed. On cytological examination, abnormally calcified microlith deposits are present in the alveolar spaces with an associated alveolar wall fibrosis and thickening. Sometimes the microliths may be in the alveolar walls and alveolar septa. Extrapulmonary abnormal calcifications are also rarely seen.
The radiological lesions of PAM can be mistaken for miliary tuberculosis, particularly in endemic areas. There are reports of patients being wrongly treated with antitubercular drugs, especially in developing countries like India.
Close radiological differentials apart from tuberculosis include stannosis, talc granulomatosis and calcified miliary histoplasmosis, metastatic calcifications, and desert sand inhalation.
There is no definitive treatment available for PAM. Treatment is largely supportive. Disodium etidronate, 10 mg/kg/day orally for a period of about 1 year has been reported to be useful. Lung transplantation is usually the last resort of treatment.
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Conflicts of interest
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