Splenic hypofunction in patients with an incidental finding of small-sized spleen at abdominal ultrasound

Abstract

Splenic hypofunction is an acquired condition, ranging from a reversible mild hyposplenism to severe splenic atrophy, and may be accompanied by a reduction in spleen size. It is potentially associated with a number of different diseases, including hematological, immunological, gastroenterological and iatrogenic disorders. Functional hyposplenism, as well as asplenia, has been shown to predispose to thromboembolic events, autoimmunity and infectious complications, the latter of which are the most widely recognized risk of these states [1]. In particular, a significantly higher relative risk of pneumococcal sepsis has been demonstrated in patients affected by splenic hypofunction or atrophy [2] due to reduced levels of circulating IgM memory B cells, a unique B cell population that needs the spleen for their survival and generation [3]. Nevertheless, the relationship between splenic function and size in hyposplenic individuals is unknown. Since a small-sized spleen can be easily detected in the course of an abdominal ultrasound examination, we aimed at evaluating splenic function through pitted erythrocyte counting in patients with an incidental finding of atrophic spleen at abdominal ultrasound. Between October 2009 and January 2011, 4,585 patients were referred to the Ultrasound Unit of our Department of Internal Medicine to undergo an abdominal ultrasound evaluation. The most frequent indications were abdominal pain (49 %), malignancy (37 %), liver and biliary disorders (10 %), bowel disorders (7 %), and nephrolithiasis (5 %). All images were obtained by an expert sonographer, using an Esaote model MyLab 70 XVG, with a 1–8 MHz convex probe and an ATL model HDI 3500, a 5.2 MHz convex probe (Philips Medical Systems, Bothel, Washington). The length of the spleen, defined as the maximum distance between the dome and the tip of the spleen, was measured on a longitudinal section with the patient in the supine or right lateral decubitus position and on deep inspiration. Patients, who were diagnosed as having a small spleen: defined as a spleen length B8 cm in men and B7.5 cm in women [4], underwent peripheral blood collection for the evaluation of spleen function. Splenic function was assessed by counting the number of pitted red cells—that is, erythrocytes bearing membrane abnormalities visible under interference phase microscopy as a so-called ‘pit’. Briefly, one drop of fresh venous blood was taken and mixed with 0.5 ml 3 % buffered glutaraldehyde solution, pH 7.4, in a plastic tube. One thousand erythrocytes were examined in a wet preparation (magnification, 1,0009) with a directinterference phase microscope Leica DMLB (Leica Microsystems Wetzlar GmbH, Wetzlar, Germany) equipped with Nomarsky optics by the same experienced observer unaware of the study. The percentage of pitted erythrocytes was calculated and taken as a measure of splenic function (upper limit of normal = 4 %) [5]. A peripheral blood sample was also collected from 52 splenectomized patients, who were used as positive controls. Data were analyzed in the GraphPad Prism statistical PC program (GraphPad Software, San Diego, CA) using the paired t test and the Mann–Whitney U test. Correlations were studied by Spearman’s rank correlation test. A level of p \ 0.05 was considered statistically significant. A small spleen was found in 203 out of 4,585 patients. Only 128 (mean age 61.5 years; 90 females and 38 males) A. Di Sabatino (&) G. Carnevale Maffe L. Brunetti M. Guerci G. R. Corazza First Department of Medicine, Fondazione IRCCS Policlinico San Matteo, University of Pavia, Piazzale Golgi 19, 27100 Pavia, Italy e-mail: a.disabatino@smatteo.pv.it