Friday, April 14, 2006

Does Restless Legs Syndrome Exist?

Those who read the essay on RLS that I linked to yesterday may find themselves wondering if RLS even exists, or if it was entirely made up by a pharmaceutical company.  Curious readers may read about it on the Merck Manual, which is a generally-respected medical handbook.  (Availably freely online here.)
Restless legs syndrome is a relatively common disorder that often occurs just before falling asleep, particularly among persons > 50 yr. The cause is unknown, but >= 1/3 of persons with the syndrome have a family history. Uncomfortable sensations that are difficult to describe are felt in the legs and are relieved temporarily by movement. Patient distress and sleep loss may become severe. Treatment can be difficult and often requires trying different drugs and dosage regimens. The drugs of choice are the dopamine agonists pergolide and carbidopa/levodopa. Other choices are oxycodone, carbamazepine, and gabapentin. Benzodiazepines taken at bedtime prevent awakening but not nocturnal movements.
Although Merck is a drug company, they do not have any drugs for RLS.  Perhaps a more objective source, though, is Harrison's Principles of Internal Medicine.  This is available online, although you have to be a medical doctor to register for it:
[...] Patients with this sensory-motor disorder report a creeping or crawling dysesthesia deep within the calves or feet, or sometimes even in the upper extemities, that is associated with an irresistible urge to move the affected limbs. For most patients with RLS, the dysesthesias and restlessness are much worse in the evening or night compared to the daytime and frequently interfere with the ability to fall asleep. The disorder is exacerbated by inactivity and temporarily relieved by movement. In contrast, paresthesias secondary to peripheral neuropathy persists with activity. The severity of this chronic disorder may wax and wane with time and can be exacerbated by sleep deprivation, caffeine, and pregnancy. The prevalence is 1 to 5% of young to middle-age adults and increases to 10 to 20% in those >60 years. There appear to be important differences in RLS prevalence among racial groups, with higher prevalence in those of Northern European ancestry. [...]

The symptoms of RLS are exquisitely sensitive to dopaminergic drugs (e.g., pramipexole 0.25 to 1.0 mg q8pm or ropinirole 0.5 to 4.0 mg q8pm), which are the treatment of choice. Narcotics, benzodiazepines, and certain anticonvulsants may also be of therapeutic value. Most patients with restless legs also experience periodic limb movements of sleep, although the reverse is not the case.[...]
Medical textbooks are not always the best source of up-to-date medical information, but Harrison's is pretty reputable, and this particular passage at least has face validity.  It would appear that in the geriatric population, the reported incidence is at least as high as that reported by the company that markets ropinirole.  However, it would appear that the company exaggerated the incidence, if one assumes that the rate they report, is a rate that applies to the general population.