|Year : 2022 | Volume
| Issue : 3 | Page : 112-114
Pulmonary alveolar microlithiasis: Lungs of stone!
N Neenu, Ketaki Utpat, Unnati Desai, Gautam Sarawade
Department of Pulmonary Medicine, Topiwala National Medical College and BYL Nair Hospital, Mumbai, Maharashtra, India
|Date of Submission||25-Apr-2022|
|Date of Acceptance||29-May-2022|
|Date of Web Publication||17-Aug-2022|
Dr. Unnati Desai
Department of Pulmonary Medicine, Topiwala National Medical College and BYL Nair Hospital, Mumbai - 400 008, Maharashtra
Source of Support: None, Conflict of Interest: None
Pulmonary alveolar microlithiasis (PAM) is a rare autosomal recessive disorder characterized by diffuse bilateral deposition of calcispherites in lung alveoli due to mutations in the SLC34A2 gene. Here, we presented a case of PAM in a young male who had been referred to our center to rule out miliary tuberculosis due to his chest radiography findings of bilateral extensive reticulonodular opacities. Possibility of PAM was considered here due to clinicoradiological dissociation and was confirmed with high-resolution computed tomography of the chest, which showed findings of Stage 2 PAM. Even though PAM has pathognomonic unique chest radiographic findings, it always poses a diagnostic challenge for physicians as it closely resembles other diseases including miliary tuberculosis, pneumoconiosis, and sarcoidosis. This case shows the need for thorough knowledge about PAM that physicians should have to reach at early prompt diagnosis and to avoid unnecessary need for invasive procedures.
Keywords: Black pleura sign, pulmonary alveolar microlithiasis, sandstorm
|How to cite this article:|
Neenu N, Utpat K, Desai U, Sarawade G. Pulmonary alveolar microlithiasis: Lungs of stone!. J Adv Lung Health 2022;2:112-4
|How to cite this URL:|
Neenu N, Utpat K, Desai U, Sarawade G. Pulmonary alveolar microlithiasis: Lungs of stone!. J Adv Lung Health [serial online] 2022 [cited 2022 Sep 25];2:112-4. Available from: http://www.jalh.com/text.asp?2022/2/3/112/353865
| Introduction|| |
Pulmonary alveolar microlithiasis (PAM) is an orphan disease with autosomal recessive inheritance along with characteristic microliths due to calcium phosphate deposits within alveolar airspace. Most commonly diagnosis made in the second through fourth decades, but has been reported in all ages. The majority of PAM cases are diagnosed incidentally on chest imaging and the disease has a slowly progressive course. No known effective treatment for the disease has been discovered yet except lung transplantation. Even if radiographic findings of PAM are highly characteristic, superficial evaluation and assessment of the radiological findings in PAM patients can lead to diagnostic dilemma with other diseases, which also present with diffuse opacification. However, the symptoms in these diseases will be more severe. Hallmark of PAM disease is the clinicoradiological dissociation. Here, we discussed one such interesting case of the rare disease PAM, its workup, and how we reached this peculiar diagnosis.
| Case Report|| |
A 30-year-old man presented with occasional dry cough with no seasonal or diurnal variation of 4 months' duration. He also reported left-sided chest pain, which was of nonradiating and dull aching in nature of 1-month duration. He had no complaints of breathlessness or fever. He had no significant family history. He had been evaluated with electrocardiogram, which was normal. The patient was a nonsmoker and bike mechanic by profession with no past medical history. His chest radiography showed bilateral extensive reticulonodular opacities [Figure 1] and he was referred to higher center for further evaluation to rule out infectious etiology. His general examination findings were normal. His respiratory system examination was also normal except for auscultatory finding of bilateral fine inspiratory crackles. Other system examination was also normal. He had normal blood parameters. His arterial blood gas analysis showed no significant abnormality. He was nonreactive for human immunodeficiency viral test. His two-dimensional echocardiography showed mild pulmonary hypertension. His 6 min' walk test distance was 560 m. His spirometry was suggestive of mild restrictive abnormality with forced vital capacity of 77% predicted and forced expiratory volume in one second of 79%. His diagnosis was further confirmed by high-resolution computed tomography (HRCT) of the thorax [Figure 2] and [Figure 3], which showed extensive bilateral reticular opacities in lung parenchyma with septal and peribronchial ossification and microcalcification with “black pleura sign” along with dense micronodules suggestive of Stage 2 PAM. He underwent flexible fiberoptic bronchoscopy, which revealed a normal bronchial tree and mucosa. He has been kept under observation as he had stable lung functions and has been asked for regular follow-up.
|Figure 1: Chest radiography showing bilateral extensive reticulonodular opacities|
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|Figure 2: HRCT thorax showing extensive reticular opacities in bilateral lung parenchyma and the black pleura sign (red arrow). HRCT: High-resolution computed tomography|
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|Figure 3: HRCT thorax with lung and mediastinal windows showing septal and peribronchial pericardial ossification and microcalcification (red arrows) along with dense micronodules suggestive of stage 2 pulmonary alveolar microlithiasis. HRCT: High-resolution computed tomography|
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| Discussion|| |
PAM is a rare disease with autosomal recessive inheritance, which is characterized by the presence of diffuse innumerable minute calculi in the alveoli of the lungs called microliths. PAM was reported by Harbitz in 1918 and accordingly it is also called Harbitz′ syndrome. The nation with the highest number of reported cases of PAM is Turkey. PAM cases are found in both the sexes and has slight male predominance. Although PAM cases are seen in all age groups, most frequently diagnosed from birth to 40 years of age. Mutations in the SLC34A2 gene causing loss of function in the sodium phosphate transporter type IIb causing accumulation of phosphate in the alveolus, leading to nidus for microlith formation is the accepted pathogenesis behind PAM. These patients will be remarkably asymptomatic and the most typical feature will be the clinicoradiological dissociation where chest radiography shows a significant “sandstorm” appearance despite a paucity of symptoms or examination findings. Symptoms of PAM usually appear by third or fourth decade of life and the most common symptoms seen are dyspnea and dry cough, but other symptoms including chest pain, hemoptysis, fatigue, and pneumothoraxes are also seen. Chest X-ray typically demonstrates sand-like calcification throughout the lungs and black pleura sign. Black pleura sign is a radiological sign in PAM seen as a strip of peripheral lucency beneath the ribs when compared to the adjacent diffusely calcified lung. HRCT findings in PAM are divided into four stages based on the degree of radiologic severity. The Stage 1 is precalcific stage and consists of few microliths and with calcification which is of low grade, only rarely observed in asymptomatic children. The Stage 2 seen in childhood or adolescence exhibits typical “sandstorm appearance” with calcific micronodules <1 mm in diameter which are scattered throughout the lungs with basal and midlung predominance. The boundaries of the heart and diaphragm appear clear. The Stage 3 is often seen in young adults, which reveals disseminated micronodules with interstitial septal thickening and crazy paving sign, and the boundaries of the heart and diaphragm are obliterated. The Stage 4 is characterized by significant advancement in the number and size of calcific deposits, leading to intense calcification of the interstitium and pleural serosa, finally giving appearance of “white lungs” seen in the later years of life. Additional HRCT findings include crazy paving pattern, calcified interlobular septa, small subpleural cysts/emphysema, and ground-glass opacities (which tend to be more common in children). Positron emission tomography scan may show high fluorodeoxyglucose uptake, but primarily in the lung regions that spare calcification. Fiberoptic bronchoscopy along with bronchoalveolar lavage showing microliths or histopathological examination of a lung biopsy is required for confirming the diagnosis of PAM. As SLC34A2 is found in other extrapulmonary sites such as kidney, prostate, pancreas, small intestine, uterus, ovary, testis, mammary glands, thyroid gland, salivary glands, trachea, liver and placenta and recently identified in human aortic valve. It causes extra-pulmonary calcifications like medullary nephrocalcinosis or nephrolithiasis, calcification of the lumbar sympathetic chain and also microliths in testes, epididymis and sympathetic ganglia, seminal vesicles of male PAM patients called testicular microlithiasis which can lead to bilateral testicular atrophy, obstructive azoospermia and can lead to infertility.,,,
The radiographic findings of PAM are highly characteristic and are extremely important for diagnosis. Radiological findings in patients with PAM can lead to diagnostic dilemma with other diseases associated with diffuse opacifications such as tuberculosis, sarcoidosis, mycosis, pneumoconiosis, amyloidosis, silicosis, healed varicella pneumonia, idiopathic pulmonary hemosiderosis, pulmonary baritosis, pulmonary stenosis, mitral stenosis, talcosis, metastatic pulmonary calcification, and amiodarone lung toxicity, which also present with, however the symptoms will be more severe in these diseases.,
Currently, no guidelines are available for the treatment of PAM. Systemic steroids, calcium-chelating agents, and bronchopulmonary lavage have shown ineffective for reducing disease progression in previous studies. Disodium etidronate was previously administered because of its possible ability to inhibit Ca3 (PO4) 2 precipitation and resolve formed calcifications. Previous studies had demonstrated its capacity to improve lung function and radiographic findings which recent other reports revealed to be ineffective. Lung transplantation can be done in the final stages of PAM and has shown improvement of right ventricular function. The survival rate and recurrence rate after lung transplantation are still under research. However, no PAM recurrences have been reported following lung transplantation till date.
Our case is one among the rare disease which poses a great diagnostic challenge for clinicians which has high radiological resemblance with other diseases such as miliary tuberculosis, sarcoidosis, and pneumoconiosis, where the evaluation treatment and management differ greatly. Our case shows the significance of the thorough knowledge of this rare disease for reaching at early correct diagnosis and thereby avoiding unnecessary invasive procedures.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient (s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]