Progressive lymphocytosis in familial hemophagocytic lymphohistiocytosis with lymphocytic interstitial pneumonia: a case report.

Familial hemophagocytic lymphohistiocytosis (FHL) is a genetically heterogeneous disorder which is less typical in adults than pediatric patients. In this study, we reported a rare case of adult-onset FHL3 with progressive lymphocytosis and lymphocytic interstitial pneumonia (LIP). A 20-year old female was admitted to our institution for persistent cough with fever. A chest high-resolution computed tomography (HRCT) scan showed diffuse bilateral ground glass opacities (GGO). A lung biopsy revealed infiltration of lymphocyte in the pulmonary interstitium. The patient was treated with corticosteroids and immunosuppressants, followed by significant clinical improvement although lymphocytosis still persisted. The definitive diagnosis of FHL was based on whole genome sequencing by which heterozygous mutations in UNC13D gene were identified. Lymphocytosis may be a remarkable feature of some patients with FHL. Performing gene sequencing is important to improve the recognition of FHL to avoid misdiagnosis.