The interactive calculator I’ve developed can be found here. Skip to the Likelihood ratios section (second tab) for the calculations used here
This conference discusses two young patients with cavitary lung lesions. The first case follows a young man with severely uncontrolled diabetes, chronic groin wound drainage after prior necrotizing infection, septic shock, and rapidly developing cavitary lung lesions. Bronchoscopy grew mucoid Klebsiella pneumoniae, raising concern for hypervirulent Klebsiella, but the case was complicated by a strongly positive serum cryptococcal antigen without clear corroborating evidence of cryptococcal disease.
The second case follows a young man with subacute cough and a new right upper lobe cavitary lesion, with exposure history notable for prior residence in Washington, travel to northern California, cross-country trips, and home renovations. Coccidioides testing returned low-positive complement fixation with negative immunodiffusion, prompting discussion of how to interpret imperfect fungal serologies in the setting of a compatible pulmonary syndrome. The teaching portion uses both cases to explore the differential diagnosis of cavitary lung lesions, the role of exposure history, pretest probability, and the difficulty of balancing empiric treatment against premature diagnostic closure.