Pulmonary alveolar microlithiasis: An ultra-rare disease

History of present illness

A 47-year-old woman complained of dry cough and dyspnea on exertion for > 10 years. Due to these symptoms, the general practitioner sent her to a primary respiratory physician. A chest radiograph was performed and showed an uncommon interstitial pattern with diffuse micronodular opacities. Consequently, the patient was referred to the center for interstitial and rare lung diseases and was hospitalized for further diagnostic procedures and treatment options.

Past medical history

The patient had no smoking history, known allergies, malignancies, or autoimmune diseases. She had hypertension, chronic renal failure, hypothyroidism, and anemia. There was no significant occupational exposure as a housewife, but she admitted contact with birds in her house. She was living in a small village in Syri, and had five children. Consanguinity was reported in the family history. Fourteen years before the admission, unspecified parenchymal lung disease had been diagnosed. She took daily medications for hypertension and hypothyroidism, as well as vitamin D supplements.

Physical examination and early clinical findings

At the admission, the patient was alert, cooperative, and afebrile (body temperature 36.8°C [98.24°F]). Oxygen saturation was 95% at room air on pulse oximetry. Her heart rate was 75 beats/min, and respiratory rate was 16 breaths/minute.

On the physical examination, skin color was pale but there was no sign of cyanosis or peripheral oedema. The chest sound was vesicular in the apical zones and diminished in the basal zones. At percussion, apical zones were resonant and lower zones were dull.

The chest radiograph findings were confirmed: there were multiple small sandlike calcific micronodular opacities (microliths, calcipherites, or calcospherites) predominantly in the basal lobes, configuring the “sandstorm lung.” A black pleural sign, which describes the vertical strip of peripheral hyperlucency between the ribs and the adjacent diffusely dense calcified lung parenchyma, was also detected. The mediastinal heart contour and diaphragm were blurred due to intensive microliths ( Fig. 15.1 A, B).

Clinical course

Blood tests showed mild renal failure (serum creatinine 1.79 mg/dL, urea 95 mg/dL) and mild microcytic anemia (hemoglobin 10.8 g/dL, mean corpuscular volume 77 fL, normal range 80–95 fL). There was no leukocytosis (white blood cell count 7210/mm ³ ) or increase of systemic inflammation markers (C-reactive protein < 5 mg/L). The platelet count was 125.000 cells/μL, international normalized ratio was 1.09. Brain-type natriuretic peptide was within the normal range (186 pg/mL). Both tuberculin skin test and QuantiFERON-TB test turned out negative.

Pulmonary function test showed mild pulmonary restriction with forced vital capacity at 73% of predicted and severe impairment of diffusing capacity of the lungs for carbon monoxide (DLCO, 27% of predicted) ( Table 15.1 ). Arterial blood gas analysis showed hypoxemia and hypocapnia with PaO ₂ 76 mmHg, PaCO ₂ 36 mmHg, and increased alveolar-arterial oxygen gradient, 31 mmHg.

TABLE 15.1 ■

Pulmonary Function Tests at Admission and in Follow-Up.

	FVC (% predicted)	FEV ₁(% predicted)	DLCO (% predicted)	Room air PaO ₂(mmHg)
At admission	66	71	27	76
At 1 year	71	67	24	65
At 2 years	73	67	26	61
At 3 years	66	69	24	59
At 4 years	65	70	22	55

FEV ₁, forced expiratory volume in 1 second; FVC, forced vital capacity; DLCO, diffusing capacity of the lungs for carbon monoxide; PaO ₂, arterial partial pressure of oxygen.

Doctors decided to perform a high-resolution computed tomography (HRCT) of the chest to better define the diffuse abnormalities detected on chest radiograph.

Chest HRCT confirmed sandstorm-like diffuse calcifications with subpleural and peribronchial distribution, particularly affecting the lower lobes and the paracardiac region. There were also ground-grass opacities with thickening of interlobular septa in both lungs and a linear radiolucency at the pleural boundaries around the heart and diaphragm ( Fig. 15.2 , A, B).