The most severe cases cause a long-term impact on mood and cognitive attention. In rare cases, patients experience long-term memory problems.In patients with KLS, MRI and CT scans show normal brain morphology. When SPECT is performed, hypoperfusion can often be observed in the brain, particularly in the thalamic and frontotemporal areas. The hypoperfusion is significantly diminished between episodes. Serum biology, c-reactive proteins and leptins, the hormonal pituitary axis, and protein in the cerebral spinal fluid (CSF) are normal in KLS patients. Cause
It is not known what causes KLS, but several mechanisms have been proposed. One possible explanation is hypothalamic or circadian dysfunction. The thalamus probably plays a role in the out-of-control sleeping, and patients with diencephalic–hypothalamic dysfunction caused by tumors experience symptoms similar to those of KLS patients. Specifically, the medial temporal regions of the thalamus may be involved, although examinations of KLS patients have not consistently found abnormalities in this area. The temporal lobe also appears to play a role in the condition, possibly causing cognitive difficulties. The apathy and disinhibition found in some with KLS suggest that the condition may include frontal lobe dysfunction as well. The involvement of the thalamus, temporal lobe, and frontal lobe of the brain suggests that there is a multifocal, localized encephalopathy. There are also persistent subclinical abnormalities in some with KLS.Another possible explanation concerns the metabolism of serotonin and dopamine. An imbalance in the neurotransmitter pathways of these chemicals could play a role. Viral infections have also been suggested as a possible cause.
History
In 1815, there was a report of a young man who showed excessive appetite and prolonged sleep after experiencing a fever; this may have been an early description of the condition. Another case with similar symptoms was described by Brierre de Boismont in 1862.Five patients with symptoms of persistent sleepiness were described in detail in 1925 by Willi Kleine, a neurologist from Frankfurt. This report was followed four years later by details of a similar case by New York-based psychiatrist Max Levin. In 1935, Levin published information about several more cases, including one described by Kleine. Levin noted that some patients displayed an intense appetite in addition to their persistent tiredness. MacDonald Critchley, who first wrote about the condition in 1942, described 11 cases he had examined and reviewed 15 other published cases in a 1962 publication. In the report, which included patients he had examined in the Royal Navy during World War II, he observed that irritability and depersonalization often occurred while patients were awake. He named the condition Kleine–Levin syndrome and noted four common traits: hypersexuality, adolescent onset, spontaneous resolution, and compulsive eating. He believed that the condition only affected males, but later studies showed some female patients. In the 1970s, several psychoanalytic and psychodynamic explanations for the condition were proposed. In 1980, a Hawaiian–Caucasian family was found in which nine family members had the condition.Diagnostic criteria for KLS was established by Schmidt in 1990, and the International Classification of Sleep Disorders further refined them.