**2. Definition of chronic ITP**

While ITP in children usually pursues an acute and self-limited clinical course that responds well to treatment, ITP in adults tends to present as a chronic relapsing condition. Traditionally, the terms chronic ITP, refractory ITP, and chronic persistent ITP are used interchangeably and are used for chronic phase of the disease. Chronic or refractory ITP was previously defined as immune thrombocytopenia persisting for >3 months, failure to respond to splenectomy, and platelet count of less than 50 x 109/L. The definition has become more confusing since the evolution of splenectomy sparing modalities of treatment.

The International Working Group (IWG) consensus panel of both adult and pediatric experts in ITP recently provided guidance on terminology, definitions and outcome criteria for this disorder (Proven et al., 2010). Primary ITP, as defined by the IWG, is platelet count less than 100 x 109/L in the absence of other causes or disorders that may be associated with thrombocytopenia. IWG used a higher platelet cutoff than the traditional criterion of 50 x 109/L based on the observation that there might be physiological variations among different racial groups and that the chances of developing persistent thrombocytopenia of less than 100 x 109/L over 10 years of follow-up seemed to be less in patients presenting with a platelet count between 100 and 150 x 109/L.

The IWG also categorizes ITP as newly diagnosed (diagnosis to 3 months), persistent (3 to 12 months from diagnosis) or chronic (lasting for more than 12 months). However, these definitions may not apply to patients with secondary forms of ITP and have not been formally validated. Specifically, "persistent ITP" includes patients not achieving spontaneous remission or not maintaining therapeutic response after stopping treatment between 3 and 12 months from initial diagnosis. The category "chronic ITP" is reserved for patients with ITP lasting for more than 12 months.

The IWG standardization does not include the degree of thrombocytopenia in classifying the different phases of the disease. The severity of disease varies in patients. Mild, moderate, and severe thrombocytopenia is used commonly in clinical practice. There are no firm guidelines. However, mild thrombocytopenia typically ranges from 50 to 100 x 109/L, moderate thrombocytopenia from 20 to 50 x 109/L, and severe thrombocytopenia under 20 x 109/L. The severity of thrombocytopenia may or may not correlate well with the risk of bleeding. It is well known that the severity and symptoms of ITP in the same patient can vary from time to time. Table 1 summarizes the different terminologies commonly used to define ITP.


Table 1. Commonly used definitions in ITP
