What predicts evolution from episodic to chronic cluster headache?

Over the last few years, attention has increasingly been focused on the evolution of cluster headache over time. Predictive factors have been identified that are correlated with an increased risk of unfavorable evolution from the episodic form to the chronic form of cluster headache. Late onset, the presence of sporadic attacks, a high frequency of cluster periods, and short-lived duration of remission periods when the headache is still in its episodic form all correlate with a possible worsening of the clinical picture over time. The reasons for evolution of episodic cluster headache to chronic are still unknown, but some factors, such as head trauma and other lifestyle factors--eg, cigarette smoking and alcohol intake--have been suggested as having a negative influence on the course of cluster headache over time.