The bone pain can also be due to necrosis. The bone marrow is very infiltrated and at some point the infiltration will cause necrosis of the bone. This is more common in the first two decades but can occur at any age. There will be severe fever, swelling, redness, warmth, tenderness at the site, with leukocytosis, decreasing hematocrit and increased ESR, and can be mistaken for an arthritis. One really has to do an MRI to be able to see necrotic lesions. Sometimes it could be the presenting sign for patients with Gaucher Disease, although this is not seen as often anymore because people with Gaucher Disease are now being treated well enough that the necrosis and the bone crisis do not arise as often as before. Patient can be very immobile for days to weeks due to these necrosis.