High resolution computed tomographic features of pulmonary alveolar microlithiasis

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Abstract

Background:

Pulmonary alveolar microlithiasis (PAM) is a rare, chronic lung disease with unknown etiology and with a nonuniform clinical course. Nonuniformity of clinical course might be related to the degree of pulmonary parenchymal alterations, which can be revealed with high resolution computed tomography (HRCT). However, HRCT findings of PAM were not fully described in the current literature.

Aim:

The aim of this study was to interpret and to contribute to describe HRCT findings of PAM and to investigate a correlation between profusion of micro nodules (MN) and pulmonary parenchymal alterations in patients with PAM.

Material and methods:

Ten male patients with PAM (mean age: 22 ± 3.2) were included into the study. HRCT images were assessed for patterns, distribution, and profusion of pulmonary abnormalities. Dividing the lungs into three zones, profusion of abnormalities was assessed. A profusion score (1–4) was given and the scores of each zone were then summed to obtain a global profusion score for HRCT ranging from 0 to 12. Also a parenchymal alteration score (PAS) was defined with respect to profusion of abnormalities. Chest X-rays were also scored.

Results:

All of ten patients with PAM had findings of interstitial lung disease in varying degrees on their HRCTs. HRCT findings of patients with PAM were as following: MN, parenchymal bands (PB), ground glass opacity (GGO) and, sub pleural interstitial thickening (SPIT) in 10 patients; interlobular septal thickening (ILST), in 9 patients; paraseptal emphysema (PSA) in 8 patients; centrilobular emphysema (CLA) in 7 patients; bronchiectasis (BE), confluent micro nodules (CMN) in 6 patients; peri bronchovascular interstitial thickening (PBIT) in 5 patients; panacinar emphysema (PANAA) in 3 patients; pleural calcification (PC) in 2 patients.

A significant correlation between MN scores and PAS (r = 0.68, p = 0.031, MN scores and GGO scores (r = 0.69, p = 0.027) and, MN scores and CLA scores (r = 0.67, p = 0.034) was detected.

We also found significant correlations between HRCT scores and results of pulmonary function tests (PFTs), HRCT scores and chest X-ray score (CXRS) and, CXRS and results of PFTs.

Conclusion:

We conclude that patients with PAM may have all findings of interstitial lung disease in varying degrees as well as MNs on their HRCTs. More importantly, this study suggests a proportional relationship between profusion of MNs and parenchymal alterations in patients with PAM. This study also suggests that the degree of parenchymal alterations closely related with the degree of pulmonary function loss in patients with PAM.

Introduction

Pulmonary alveolar microlithiasis (PAM) is a rare, chronic lung disease with unknown etiology characterized by extensive intra-alveolar spherical calcium and phosphate deposition throughout both lung parenchymas.

The incidence of PAM is high in certain countries such as Turkey, Italy and USA [1], [2]. Patients with PAM usually show sand like micro nodular infiltration particularly marked at lower zones predominantly at para cardiac areas in their chest X-rays. Since there is a surprising discordance between chest X-ray findings and clinical presentation, chest X-ray is almost pathognomonic for the diagnosis of PAM [1], [2], [3]. Even though pulmonary parenchyma can be examined much more detailed with high resolution computed tomography (HRCT) than chest X-ray, HRCT findings of PAM were not fully described in the current literature. There are several studies indicating CT findings of PAM such as thickening of interlobular septa, thickening of peri bronchovascular interstitium, ground glass opacity, paraseptal emphysema etc. but most of which were based on single case or few case reports [3], [4], [5], [6], [7], [8], [9].

PAM has not a uniform clinical beginning and a uniform clinical course [2], [3]. Nonuniformity of clinical features might be related to pulmonary parenchymal alterations in patients with PAM.

Cases at early stages of the disease show a surprisingly intact lung parenchyma and the disease is initially endoalveolar and then undergoes progression with the development of parenchymal alterations [3], [10].

We hypothesized that there might be a relationship between profusion of micro nodules (MN) and pulmonary parenchymal alterations in patients with PAM.

The aim of this study was to interpret and to contribute to describe HRCT findings of PAM and to investigate a correlation between profusion of MNs and pulmonary parenchymal alterations in patients with PAM.

Section snippets

Material and method

Inpatient records from 1998 to 2004 were screened to find out patients with a diagnosis of PAM in archive of Department of Pulmonary Medicine in Gulhane Military Medical Academy. Eight patients were found recorded with a diagnosis of PAM. In addition to these eight patients there were two recently diagnosed patients who were examined prospectively. A total of 10 patients with PAM were included into the study. All patients were male and their mean age was 22 ± 3.2. None of the patients had a

Method of diagnosis

Five of eight patients and two new patients were diagnosed based on histopathological, radiological and clinical findings, while three patients’ diagnosis were based on radiological and clinical findings. Fiberoptic bronchoscopy and transbronchial biopsies yielded histopathologic diagnoses in seven patients. Histopathologic findings of transbronchial lung biopsy showed concentric lamellar calcified microliths with hematoxylin–eosin stain (Fig. 1). Fiberoptic bronchoscopy had not been performed

Discussion

We have shown that patients with PAM may have all kind of features of interstitial lung disease on their HRCTs in varying degrees; in some patients ILST was the prominent feature, in the others PB and in some CLA and so on. PAM has not a uniform clinical beginning and a uniform course. Some patients may have symptoms some patients not. It has a worse prognosis in some patients resulting with death as a consequence of respiratory failure than some patients with a very long silent period of the

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