The influence of clinical features mimicking primary immunodeficiency diseases (mPID) on children with Langerhans cell histiocytosis (LCH) — Four with mPID among 39 LCH children from one referral center during 18-year period

Background: Recurrent or refractory infections can be a warning sign of primary immunodeficiency diseases (PID). Such mimicking PID (mPID) can occur in patients with Langerhans cell histiocytosis (LCH). Because some cases with refractory molluscum contagiosum-like lesions and persistent otorrhea are finally diagnosed with LCH, we wondered whether such mPID can occur in LCH children and affect on their prognosis. Methods: We retrospectively reviewed all children with LCH at our institute from 2001 to 2018. A complete medical review of sex, age, symptoms, treatment course, and outcome comparison was performed. Results: Of 39 enrolled LCH patients, three had persistent otorrhea and one had refractory molluscum contagiosum-like lesions despite aggressive antibiotic therapy. These four cases with mPID had significantly higher rates of multi-system involvement, recurrence and 5-month more lag time, but no risk organ (liver, spleen and bone marrow) involvement compared to those without mPID, although bone and skin were the most involved in both groups. Overall, the lag-time in multi-system was longer than that in single-system involvement (median 2.5 vs. 1.0 months; p = 0.003). The diagnosis-age of risk organ involvement was younger than those without (median 8 vs. 43 months; p = 0.004). There were no significant differences in diagnosis-age, single/multi-system and risk organ involvement between remission and recurrence groups. All were alive excluding four who were lost to follow-up. Conclusions: The LCH children with mPID had greater lag time, multi-system involvement, recurrence and more refractory treatment including transplantation despite the ratio of bone and skin lesions equal to those without mPID.