A 34-year-old woman presents with progressive dyspnoea on exertion over 18 months. Spirometry shows FEV1/FVC ratio of 0.62 with FEV1 of 58% predicted. DLCO is markedly reduced at 45% predicted. High-resolution CT chest reveals diffuse, bilateral, thin-walled cysts of varying size uniformly distributed throughout both lungs with preserved intervening parenchyma. The spirometric and imaging findings marked **A** in the diagram are consistent with which diagnosis?
A. Hypersensitivity pneumonitis
B. Pulmonary Langerhans cell histiocytosis
C. Lymphangioleiomyomatosis (LAM)
D. Centrilobular emphysema
Explanation
Why Lymphangioleiomyomatosis (LAM) is right
The combination of obstructive spirometry (reduced FEV1/FVC), markedly reduced DLCO disproportionate to the degree of obstruction, and characteristic HRCT findings of diffuse, bilateral, thin-walled cysts uniformly distributed throughout both lungs in a young woman is pathognomonic for LAM. According to the ATS/JRS 2016 Clinical Practice Guideline, LAM is a rare, low-grade metastasizing neoplasm of smooth-muscle-like cells that occurs almost exclusively in women of reproductive age (mean diagnosis 35 years). The obstructive pattern with reduced DLCO reflects alveolar destruction and pulmonary vascular involvement from proliferation of LAM cells around airways and lymphatics. The uniform distribution of thin-walled cysts with preserved intervening parenchyma distinguishes LAM from other cystic lung diseases.
Why each distractor is wrong
Pulmonary Langerhans cell histiocytosis: While it also presents with cystic lung disease, HRCT shows cysts AND nodules with upper-lobe predominance and basal sparing in smokers. The uniform distribution throughout both lungs without nodules and the clinical presentation in a non-smoker make this unlikely.
Centrilobular emphysema: Emphysema does not produce thin-walled cysts with visible walls on HRCT; the cysts in emphysema lack walls. The marked reduction in DLCO disproportionate to obstruction and the uniform cyst distribution are not typical of emphysema.
Hypersensitivity pneumonitis: This typically presents with a restrictive pattern (reduced FEV1/FVC is not expected) and ground-glass opacities or nodules rather than diffuse thin-walled cysts. The spirometric pattern and imaging are not consistent with this diagnosis.
High-YieldNEET PG
LAM in a young woman with obstructive spirometry, disproportionately reduced DLCO, and diffuse bilateral thin-walled cysts uniformly distributed on HRCT — think LAM and check for spontaneous pneumothorax history, renal angiomyolipomas, and serum VEGF-D (>800 pg/mL is highly specific).
ATS/JRS Clinical Practice Guideline for LAM 2016; MILES trial NEJM 2011
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