FCEM-1620

A 62-year-old woman presents with a 3-month history of lethargy and tiredness. She states that she has also felt very itchy, particularly after a hot bath and that she is often dizzy and sweaty. On examination she appears plethoric and you note the presence of splenomegaly. Her blood tests today show that her haemoglobin level is 16.9 g/dl.What is the most likely diagnosis in this case? Select ONE answer only.