Importance of excluding invasive aspergillus infection prior to immunosuppression

We read the intriguing report by Kumar and Gupta regarding a case of false positive AFB subsequently diagnosed as granulomatosis with polyangiitis in a patient with respiratory symptoms and bilateral cavitating nodules on chest imaging. ¹

The serum galactomannan antigen level was found to be remarkably elevated at 2.7 (reference <0.5) in the workup described for that patient. Serum and bronchoalveolar lavage (BAL) galactomannan antigen are primarily used in the diagnosis of invasive aspergillosis (IA) for which these tests are part of the microbiological diagnostic criterion.^2,3 We note that a BAL sample was sent for microscopy with fungal staining which was reported to be negative. It would be prudent to detail if further workup was done to exclude an underlying fungal etiology, for example, BAL fungal culture, BAL galactomannan antigen level and BAL sample testing for aspergillus PCR, as the immunosuppression used for the treatment of granulomatosis with polyangiitis could have worsened an undiagnosed underlying aspergillus infection. IPA has a high mortality and it can be up to 80% in patients with haematological malignancies ventilated in the ICU. ⁴

Some of the factors reported to cause false positive serum galactomannan include colistin inhalation treatment and beta-lactam antibiotic treatment.^5,6 To our knowledge and literature search, neither the initial presumed diagnosis of TB nor the final diagnosis of granulomatosis with polyangiitis has been reported to cause raised serum galactomannan levels.

It is reassuring that the patient described in this case report was stable on follow-up visit, however it would be interesting to know whether an alternate etiology for the raised serum galactomannan levels was confirmed and a diagnosis of aspergillus excluded before commencing immunosuppression. Perhaps serum galactomannan can be rechecked on follow-up patient visits to ensure that it was a false positive result.