Is most often caused by allergic disorders or parasitic infections, but other causes are also possible, for example. autoimmune diseases, dermathology deseases, Hodgkin's disease. When the cause is not identified, we talk of the hypereosinophilic syndrome which is near to myeloproliferative disorders.
The marrow is normo- or hypercellular with an elevated eosinophil count. Other lineages remain normal.