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Background Hyper IgM syndromes (HIGMS) are a group of rare primary immunodeficiency disorders. There are limited reports about HIGMS combined with severe eosinophilia. Case presentation In this report, we described a 2-year-old boy with chronic cough and symptoms of hypoxia. Lung computed tomography (CT) scan showed that diffuse ground-glass changes and eosinophils in peripheral blood increased significantly. Subsequent tests revealed a notable decrease in serum IgG and IgA. The lymphocyte subgroup classification was basically normal. Pneumocystis jirovecii were detected from the bronchoalveolar lavage fluid (BALF) of the patient by metagenomic next-generation sequencing (mNGS). After treatments of caspofungin combined with sulfamethoxazole, intravenous immunoglobulin (IVIG) replacement and anti-inflammatory steroid, the clinical symptoms and pulmonary imaging noticeably improved. The absolute eosinophil count (AEC) also returned to normal range. X-linked hyper IgM syndrome was confirmed by gene test. Two months after the diagnosis, the patient underwent allogeneic stem cell transplantation (HSCT) and has recovered well. Conclusions Children with HIGMS are prone to opportunistic infections such as Pneumocystis jirovecii pneumonia (PJP). Diffuse interstitial lung disease and hypoglobulinemia in a young child predict the diagnosis of a primary immunodeficiency (PID). mNGS has obvious advantages for obtaining etiological diagnosis of children with PIDs. Severe eosinophilia is rarely reported in this kind of PIDs. Considering literature review and the corresponding reaction to steroid, we proposed that eosinophilia in HIGMS might be related to infections. Steroid therapy can quickly relieve eosinophilia but is easy to rebound if the reduction is too fast. Once the diagnosis of HIGMS is confirmed, the earlier the HSCT, the better the prognosis.

Activated phosphoinositide 3-kinase-δ syndrome 1 (APDS1) is a combined immunodeficiency caused by a heterozygous gain-of-function mutation in PIK3CD, encoding the p110δ catalytic subunit of phosphoinositide 3-kinase δ (PI3Kδ). APDS1 is characterized by recurrent sinopulmonary infections, leading to airway damage, chronic herpes viremia, lymphoproliferation, and autoimmune and inflammatory diseases. Several cases of systemic lupus erythematosus (SLE) have been reported in APDS1; however, Sjögren's syndrome (SS) or an SS-like phenotype is rarely described in patients with APDS1. In this study, we report a 4-year-old girl with APDS1 who did not experience recurrent sinopulmonary infections and chronic viremia but presented with cytopenia, proteinuria, hypocomplementemia, and positive antinuclear antibodies that met the classification criteria for SLE. Additionally, the patient also mimicked a secondary SS-like phenotype based on recurrent parotitis and labial salivary gland biopsy. The patient achieved remission after treatment with sirolimus and immunosuppressive therapy. This case report enriches the clinical phenotype of APDS1 and provides a reference for the diagnosis and therapy of patients with APDS1.

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