Clinical diagnosis
Case 273
【Progress】
She was given steroid pulse treatment using methyl prednisolone 500mg X 2/day for 3 days and thereafter, steroid reduce and maintenance therapy.
【Discussion】
Acute interstitial pneumonia (AIP) is characteristic of bilateral ground glass opacity with crazy paving pattern (melon skin appearance) that is more prominent in lower lobes rather than upper lobes on CT (1). Meanwhile, cardiac congestion is also characteristic of bilateral ground glass or consolidation called butterfly pattern on CT which is, more prominent in upper lobes rather than lower lobes.
AIP is one of the diseases causing acute respiratory distress syndrome (ARDS). ARDS is basically a condition of respiratory failure and categorized into three according to PF ratio: 200 < mild ≤ 300 , 100 < moderate ≤ 200 and severe ≤ 100 (2). The basic histologic finding of ARDS is diffuse alveolar damages (DAD)(2, 3). The diseases causing ARDS or DAD are AIP, hypersensitivity pneumonitis, drug-induced pneumonitis, infection of virus and bacillus, exacerbation of usual interstitial pneumonia (2).
AIP is the synonym of Hanman Rich syndrome which is defined as unknown origin with poor prognosis, almost 50% mortality rate (3, 4). As described above, histologic findings are DAD, indicative of increase of KL 6 for secreting or damaging type II alveolar cells and of LDH increase for damaging type I alveolar cells on laboratory test. Patients with AIP fall into respiratory failure instantly and lethal. When patients with AIP survive, clinical stages change from exudative phase, organization phase and fibrotic phase. CT images reflect these phases: ground glass opacity and/or melon skin appearance (crazy paving pattern) on exudative phase, reticular fibrosis on organization phase and fibrotic honey comb pattern with tractional bronchiectasis on fibrotic phase (3, 5-8).
In the process of ARDS, it is crucial to recognize that ground glass opacity and melon skin appearance are not just caused by alveolar cell damages but also by interstitial edema caused by pulmonary hypertension (PH)(9, 10). The definition of PH is that pulmonary artery pressure is more than 25 mmHg or greater: borderline PH is 20 < < 25mmHg; normal PH is ≤ 20 mm Hg (9, 10). CT images reflect PH when main pulmonary artery diameter is > 33 mm or greater, borderline PH 29 mm ≤ ≥ 32 mm and normal < 29 mm. Further, main pulmonary artery diameter / ascending aorta ratio 1 or greater indicates pulmonary hypertension (11-15). Then, when ground glass opacity and melon skin appearance is shown in symmetric bilateral lobes on CT, not just interstitial pneumonia but also pulmonary hypertension should be considered by checking the diameter of main pulmonary artery and the ratio of main pulmonary artery to ascending aorta. When right ventricle strains burdening to cope with pulmonary hypertension, laboratory test should reveal elevation of values of BNP (brain natrium peptide) and troponin. Then, clinicians should watch to not just pulmonary area but also pulmonary artery on CT and moreover, laboratory values of KL-6, LDH, BNP and troponin.
In our case, CT showed ground glass opacity and melon skin appearance found in bilateral lower lobe rather than bilateral upper lobes. KL-6 value elevated and the ratio of main pulmonary artery to ascending aorta is less than 1.0, indicative of alveolar cell damages and less pulmonary hypertension.
【Summary】
We presented an eighty three year-old female for dyspnea and suspicious pneumonia. Laboratory test revealed KL6 1282 U/mL, SPD 253 ng/mL < 110 and CT showed bilateral ground glass opacity with crazy paving pattern more predominant in the lower lobes rather than upper lobes, indicative of not cardiac failure but acute interstitial pneumonia. It is borne in mind that when bilateral opacity with crazy paving pattern is shown on CT, it is crucial to check whether it is more predominant lower lobe or not, to check diameter of pulmonary artery and that of ascending aorta on CT and further to check laboratory test: KL-6, LDH, BNP and troponin. It is crucial to check them whether these findings come from pulmonary parenchyma origin, pulmonary artery hypertension origin or cardiac failure origin.
【References】
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