Correct!
4. c-ANCA antibody assessment and renal biopsy
Positive c-ANCA testing is suggestive of the diagnosis of granulomatosis with polyangiitis, but is not specific for that diagnosis and the absence of c-ANCA positivity does not exclude the diagnosis of granulomatosis with polyangiitis. Therefore, a tissue diagnosis from an area of active inflammation is preferred to establish the diagnosis of granulomatosis with polyangiitis conclusively. Given the clinical evidence of renal involvement in this patient, renal biopsy could provide tissue to confirm the diagnosis of granulomatosis with polyangiitis. Bronchoscopy with transbronchial biopsy may be able to provide a tissue for diagnosis also, but the amount of tissue obtained with this procedure is relatively small and may be insufficient to establish the diagnosis of granulomatosis with polyangiitis, and the larger amount of tissue that may be procured with renal biopsy may be preferable. Percutaneous transthoracic fine needle aspiration biopsy often provides a larger amount of tissue for diagnosis compared with bronchoscopy and transbronchial biopsy, but is associated with a higher complication rate. Neither serial thoracic CT to assess for growth or change in the cavities and nodules nor 18FFDG-PET scanning would provide management-altering information in this patient. The patient clearly has an active, undiagnosed pulmonary parenchymal process, and therefore follow up imaging is not appropriate, and the presence of absence of glucose utilization within the pulmonary lesions would not mitigate the need to establish a diagnosis immediately.
The patient subsequently underwent c-ANCA testing, which was positive, and percutaneous renal biopsy showed segmental necrotizing glomerulonephritis with crescent formation.
The most likely diagnosis for the lesions in this patient is which of the following?