The primary purpose of this study is to determine the effects of ruxolitinib on spleen size and symptoms and to learn about any of the side effects that might occur during or following treatment. This study will also help us determine the appropriate dosing for patients with low platelets. To see if ruxolitinib is having any effect on your disease we will collect other blood samples called biomarker or, in this study, pharmacodynamic samples. During the screening phase, tests including blood draws, bone marrow biopsy, physical exam, MRI/CT as necessary, will be done to determine a patient's eligibility. The treatment phase consists of 24 weeks where patients will take the study drug and come to MUSC for tests including blood draws, physical exams, genetic testing etc to measure how the pt is responding to treatment. Subjects may continue to receive treatment after 24 weeks if their doctor agrees that this is appropriate.