Clinical features of chronic summer-type hypersensitivity pneumonitis and proposition of diagnostic criteria

Background: Trichosporon asahii (T. asahii) causes chronic summer-type hypersensitivity pneumonitis (C-SHP); however, little is known about the clinical features of this condition. We aimed to elucidate the clinical features of C-SHP and propose practical diagnostic criteria for C-SHP based on the presence of serum anti-T. asahii antibody (TaAb).

Methods: Patients diagnosed with C-SHP and idiopathic pulmonary fibrosis (IPF) between January 2010 and May 2017 were reviewed retrospectively. Clinical findings were compared between the two groups. Criteria for C-SHP were proposed on the basis of significant characteristics and applied to the development and validation cohorts.

Results: Thirty-one patients with C-SHP and 26 with TaAb-negative IPF were identified. C-SHP patients were more likely to live in wooden houses; their serum Krebs von den Lungen-6 (KL-6) and serum surfactant protein-D (SP-D) levels were higher than those of IPF patients. C-SHP patients were more likely to have subpleural consolidation, micronodules, and extensive ground-glass opacification on high-resolution computed tomography (HRCT). The following 3 items were considered to have diagnostic value: I) TaAb positivity; II) an HRCT pattern consistent with chronic hypersensitivity pneumonitis, including mosaic attenuation or micronodules; and III) elevated serum biomarker levels (KL-6 > 1500 U/mL or SP-D > 250 ng/mL). We defined cases satisfying I) and II) as "probable C-SHP" and those satisfying all 3 criteria as "confident clinical diagnosis of C-SHP". The areas under the receiver-operating curve were 0.965 and 0.993 in the development and validation cohorts, respectively, which suggested that these criteria had good discriminative ability in clinical evaluations.

Conclusions: Clinical features could be useful for distinguishing C-SHP from IPF and other etiologies of ILDs.