A cough that doesn’t fit the mould

Editor – We read with interest the lesson of the month regarding invasive pulmonary aspergillosis in an immunocompetent patient.¹ We wish to highlight two points.

First, the normal range (<40 mg/L) used for Aspergillus IgG was extrapolated from a study of 130 patient specimens, which was originally designed to compare the validity of an IgG assay against the standard double effusion test.² In order to investigate the utility of Aspergillus IgG levels in a clinical setting, we recently carried out a study of IgG levels in age-matched sera from two groups; a respiratory group with clinical suspicion of chronic pulmonary aspergillosis and a control group.³ A total of 696 IgG levels were available, 348 from each group. The arithmetic mean IgG titre was 37.4 mgA/L (log₁₀; 1.40) in the respiratory group and 22.4 mgA/L in the control group (log₁₀; 1.15) (p<0.0001), although the group populations became aligned after accounting for quality assurance variation during the tests. We concluded that a significant overlap in levels does not allow the determination of a discriminatory cut-off value, and therefore interpretation of IgG should be used with caution.

Second, the authors stated that the duration of treatment would typically last at least 3 months. However, the duration of therapy has not been optimally defined.⁴ Three months of voriconazole would cost approximately £7,000⁵ per patient and long-term voriconazole may expose patients to unwanted side effects.

We hope that these two points highlight issues for consideration in the clinical setting of the diagnosis and treatment of suspected invasive pulmonary aspergillosis and we wondered to what extent long-term voriconazole is required following successful physiotherapy and mucus plug removal?