The literature reports various experiences on the use of shear wave elastography (SWE) in the study of the intestine, especially in patients with chronic inflammatory bowel diseases. But few data are reported on the use of the method in patients with graft versus host disease. Considering the simplicity of the method, we think it can be applied to an ultrasound study of the intestine to try to understand the potential of SWE to further define the characteristics of the intestinal segments involved.

Study population will include all patients submitted to allogenic stem cell transplantation (SCT) who developed diarrhea \> 500 ml per day suggestive for aGvHD until 100 days from transplant date. Patients submitted to autologous stem cell transplant who developed diarrhea between transplant date and engraftment achievement will constitute control population as for other infectious complications assessment. Within 24-48 hours from symptoms, onset full panel of stool cultures will be performed together with Clostridium toxin assessment. Multiparametric ultrasound study will be performed at the onset of the symptoms and then weekly to monitoring intestinal changes accordingly to symptoms evolution during treatment. In the case with high suspicion for aGvHD (stool culture negative, persistent or progressive diarrhea, ultrasound imaging closely suggestive for aGvHD), as per common clinical practice, colonoscopy will be required to evaluate internal macroscopy features of the bowel and to obtain histological samples for conclusive diagnosis. In the meantime steroid therapy will be started, as per common clinical practice. The only modification of this protocol to common clinical practice is represented by the addition of a non-invasive bed-side method of evaluation of the patients with diarrhea. None of the routinely performed diagnostic and therapeutic process will be modified. All patients submitted to autologous stem cell transplant who developed diarrhea between transplant date and engraftment achievement will constitute control population. Also in this case full panel of stool culture and clostridium toxin assessment will be performed at the onset of the symptoms. Multiparametric ultrasound study will be made al symptoms onset and then weekly until symptom resolution. Multiparametric ultrasound study will be performed by expert qualified staff as following:The examinations will be performed at patient's bed, in supine position, with a MyLab™9 Platform (by Esaote corporate, Italy) system. Fasting is required.

US for bowel requires both low-frequency convex probes (3.3-5 MHz) and high-frequency (5-17 MHz) linear assay probes to increase the spatial resolution of the intestinal wall and to assess the wall diameter and wall layer.

Primary endpoint of the study is to evaluate the accuracy of bed-side multiparametric ultrasound study in the diagnosis of gastrointestinal aGvHD in patients underwent to allogenic transplant in terms of sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV). Secondary endpoints To assess potential associations between bed-side multiparametric ultrasound measurements weekly performed and aGvHD diagnosis in patients underwent to allogenic transplant. To assess whether bed-side multiparametric ultrasound measurements at baseline differ in distinguishing complications different from aGvHD (i.e., infectious, drug-related o neutropenic colitis) in patients underwent allogenic transplant as compared to auto-transplant