A precursor of the measles began causing infections in humans as early as the 4th century BC or as late as after AD 500. The Antonine Plague of AD 165–180 has been speculated to have been measles, but the actual cause of this plague is unknown and smallpox is a more likely cause. The first systematic description of measles, and its distinction from smallpox and chickenpox, is credited to the Persian physician Muhammad ibn Zakariya al-Razi (860–932), who published The Book of Smallpox and Measles. At the time of Razis book, it is believed that outbreaks were still limited and that the virus was not fully adapted to humans. Sometime between AD 1100 and 1200, the measles virus fully diverged from rinderpest, becoming a distinct virus that infects humans. This agrees with the observation that measles requires a susceptible population of >500,000 to sustain an epidemic, a situation that occurred in historic times following the growth of medieval European cities. Measles is an endemic disease, meaning it has been continually present in a community and many people develop resistance. In populations not exposed to measles, exposure to the new disease can be devastating. In 1529, a measles outbreak in Cuba killed two-thirds of those indigenous people who had previously survived smallpox.
Periodic limb movement disorder (PLMD) is a sleep disorder where the patient moves limbs involuntarily and periodically during sleep, and has symptoms or problems related to the movement. PLMD should not be confused with restless legs syndrome (RLS). RLS is characterized by a voluntary response to an urge to move legs due to discomfort. PLMD on the other hand is involuntary, and the patient is often unaware of these movements altogether. Periodic limb movements (PLMS) occurring during daytime period can be found but are considered as a symptom of RLS. Only PLMS during sleep can suggest a diagnosis of PLMD.Periodic limb movement disorder is characterized by recurrent episodes of frequent limb movements while sleeping. It mostly happens in the lower parts of the body like the toes, ankles, knees and hips. It can also, in some cases, appear in the upper extremities of the body. These movements can lead the patient to wake up, and if so, sleep interruption can be the origin of excessive daytime sleepiness.PLMD is characterized by increased periodic limb movements during sleep (PLMS), which must coexist with a sleep disturbance or other functional impairment, in an explicit cause-effect relationship. Usually, these involuntary movements come from lower extremities (including toes, ankles, knees, and hips), although they can also be observed in upper extremities, occasionally. PLMS seem to be common features within many people, and identifying whether or not these movements are clinically relevant for a distinct diagnosis of PLMD remains a challenge for clinical and scientific fields.