• Epidemiology
• migraine
• movement disorders

Migraine is associated (comorbid) with a number of neurological (epilepsy, stroke) and psychiatric (depression, mania, anxiety, panic) disorders.1 It is now known to be comorbid with restless legs syndrome (RLS) as well. Migraine comorbidity is important for a number of reasons. When illnesses are comorbid, the principle of diagnostic parsimony does not apply: the presence of migraine should increase, not reduce, the suspicion that another disorder may be present. Comorbidity is important when developing treatment strategies. A comorbid illness provides therapeutic opportunities, but it also imposes therapeutic limitations. Some treatments may be relatively contraindicated in individuals who have more than one disease.

Restless legs syndrome is a disorder of motor restlessness associated with paraesthesia/dysaesthesia in the arms or legs that affects up to 10–15% of the population.2 Symptoms are relieved with activity and exacerbated by rest.3 It is most commonly idiopathic but can be secondary to other neurological disorders.4 While no comprehensive explanation of the pathophysiology of RLS exists,5 evidence suggests that it may be secondary to a central hypodopaminergic state. Direct dopamine stimulation with either carbidopa/levodopa or dopamine agonists is effective in relieving the symptoms of both idiopathic and secondary RLS.6–13 In addition, both PET14 and SPECT15 studies implicate diminished striatal dopamine binding in RLS and periodic limb movements of sleep. Some RLS patients have low ferritin levels and may benefit from iron therapy. The D₂ receptor contains iron, …