The chicken or the egg of lymphopenia in atopic eczema.

Abstract

Lymphopenia has been documented in atopic eczema (AE) patients mostly in the setting of an active infection.1, 2 However, the question is whether lymphopenia is a primary problem in AE leading to infection or it is a secondary problem due to infection. In the study by Hollestein et al.,3 the authors conducted a retrospective review of a large electronic database (UK primary care electronic health record from CPRD GOLD). They included 71,731 adults with AE and 126,349 adults without AE. Using the definition of lymphopenia as having two lymphocyte counts of <1 × 109/L in 3 months, they showed that 4.1% (n = 2909) of AE patients had lymphopenia as compared to 3.7% (n = 4700) of controls without AE. The adjusted OR for lymphopenia in AE patients as compared to those without AE was 1.16 and this increased to 1.89 in patients with severe AE. Their data were appropriately adjusted for age, sex, ethnicity, smoking, co-morbidities and immunosuppressive drug use. In their secondary analysis, they confirmed an increased risk of skin and systemic infections including cellulitis, varicella zoster, gastroenteritis and urinary tract infection in AE patients as compared to controls. The authors also replicated their findings of lymphopenia in AE patients based in a US database, NHANES. Their data support the hypothesis that lymphopenia may predispose to increased infections in AE patients. A possible mechanism of lymphopenia in AE patients is due to the homing of systemic lymphocytes to inflamed skin. Their finding of a higher risk of lymphopenia in more severe AE is also consistent with this mechanism. While Hollestein et al. have provided a robust and well-controlled study that lymphopenia may be a primary problem in AE patients, the findings can only be inferred as an association, rather than cause-and-effect, due to the retrospective nature of the study. In a real-life clinical situation, complete blood cell (CBC) profile is normally sent when a patient is symptomatic, that is, during an illness or an infection. Acute lymphopenia is common with viral respiratory infections.4 In AE patients, CBC may also be sent together with viral or bacterial identification testing during a skin infection, which may be associated with lymphopenia.1, 2 AE patients are not known to have a primary immunodeficiency that predisposes them to have increased infection. However, skin and soft tissue infections are more common in AE patients due skin barrier defects and suppression of cutaneous innate immunity by type 2 cytokines.5 The results of Hollestein et al. are nevertheless interesting, and will need to be confirmed with prospective studies. None to declare. P. Ong reports no conflict of interest relevant to this article. Data sharing not applicable.