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2. The thoracic CT shows extensive smooth interlobular septal thickening
The thoracic CT shows extensive, basal predominant, smooth and regular linear opacities reflecting smooth interlobular septal thickening (Figure 4).
Figure 4. Thoracic CT displayed in lung windows through the mid and lower lungs shows smooth interlobular septal thickening (arrowheads), becoming particularly pronounced in the bases bilaterally.
The central and peripheral airways appear normal- there is no evidence of bronchiectasis. No features of fibrotic lung disease, such as traction bronchiectasis, lobular distortion, honeycomb lung, architectural distortion, and coarse reticulation, are evident. Smoking-related pulmonary diseases may present in variable fashion on thoracic CT, often with features of obstructive lung disease, particularly emphysema, superimposed. Respiratory bronchiolitis typical manifests as upper lobe, small, centrilobular nodules in an asymptomatic patient. Respiratory bronchiolitis-interstitial lung disease occurs in symptomatic, usually heavy smokers, typically shows findings such as bronchial wall thickening, multifocal ground-glass opacity, upper lobe predominant ground-glass opacity centrilobular nodules, and air trapping at thoracic CT. Desquamative interstitial pneumonia usually presents as multifocal, sometimes peripherally predominant, ground-glass opacity, occasionally associated with cystic foci. Langerhans cell histiocytosis usually presents as upper lobe predominant nodules that eventually undergo cystic change and cavitation, eventually resulting in thin-walled cysts resembling severe, confluent, centrilobular emphysema. Combined pulmonary fibrosis and emphysema presents with upper lobe emphysema and lower lobe fibrotic findings. An emerging literature detailing other patterns of smoking-related interstitial abnormalities, variously referred to as respiratory bronchiolitis with fibrosis, air space enlargement with fibrosis, and smoking-related interstitial fibrosis, may manifest as upper lobe predominant emphysema associated with interstitial thickening and reticulation, sometimes simulating a cystic appearance, or as upper lobe predominant emphysema with lower lung ground-glass opacity; none of these presentations are evident in this patient. Thoracic CT features of active pulmonary infection various include focal, multifocal, or diffuse ground-glass opacity and / or consolidation, bronchial wall thickening, and small nodules, occasionally with branching configurations- no such abnormalities are seen in this patient).
A more focused history and physical examination was performed and additional laboratory evaluation was pursued. Hepatosplenomegaly was detected, and it was noted that the patient was thrombocytopenic.
What it the most likely relevant historical point discovered as a result of the focused history? (Click on the correct answer to proceed to the next panel)