Haemophagocytic lymphohistiocytosis in Hong Kong children have a wider clinical spectrum.

To the Editor—We read with interest Chan et al’s report on haemophagocytic lymphohistiocytosis (HLH) in Hong Kong children.1 Of their seven cases, none was classified as primary HLH but limited by unavailability of molecular testing. No malignancy or connective tissue disease was found. Two of seven were confirmed by serology testing to have EpsteinBarr virus (EBV)–associated HLH. The mean time from onset of fever to initiation of treatment was 24 days. The overall survival rate was 43%. We reviewed our experience during the same period (1991-2006).2-4 Nine patients (male:female, 5:4; mean age, 7 years) were diagnosed according to guidelines.5 Their clinical features, laboratory findings, viral aetiology, treatment and outcome are summarised in the Table. Two boys from the same family had X-linked lymphoproliferative disorder triggered by primary EBV infection. The signalling lymphocytic activation molecule–associated adaptor protein (SAP) gene deletion was confirmed.3 The older brother died of multi-organ failure and the younger one was successfully transplanted with mismatch-unrelated cord blood. One had macrophage activation syndrome due to adult-onset Still’s disease.4 One had anaplastic large-cell lymphoma. One had malignant histiocytosis and died of cerebral mucomycosis. She had trisomy 3 by cytogenetic analysis of bone marrow. Four had primary EBV infections alone by serology and EBV DNA measurement in plasma and bone marrow.2,3 With a mean time of 21 days from onset of fever to initiation of etoposide, steroid with or without cyclosporin-based treatment, the overall survival rate was 78% (median follow-up, 6 years). We reckon relying solely on serological diagnosis could be misleading as these patients may have defective antibody production. Genome quantification of EBV is perhaps warranted in HLH.