When should "chronic migraine" patients be considered "refractory" to pharmacological prophylaxis?

Patients with chronic headache forms evolving from a previous episodic migraine ('chronic migraine') are often difficult to treat. In this paper we focus attention on aspects we believe important for producing a definition of "refractory" in relation to this headache form. We propose a "chronic migraine" patient should be considered "refractory" to pharmacological prophylaxis when adequate trials of preventive therapies at adequate doses have failed to reduce headache frequency and improve headache-related disability and, in patients with medication overuse, reduce the consumption of symptomatic drugs. However before a definition of "refractory" chronic migraine can become established, generally accepted diagnostic criteria and treatment guidelines for this condition need to be developed.