Nodding syndrome is an epileptic disorder, with telltale nodding episodes caused by atonic seizures, concludes a pioneering study of the mysterious neurologic illness that has been reported in only three African countries.
The study, published in The LancetNeurology, looked at cases emerging from an epidemic pattern of the disease in northern Uganda and is the first to systematically assess the clinical features, short-term outcomes, and epidemiology of this rare neurologic disorder.
Most of 23 children - 7 to 15 years of age - who experienced daily head nodding experienced seizures while 30% had gross cognitive impairment. In a larger group of 78 children, head nodding generally predicted global cognitive impairment, such as slowed reaction and dull affect, relative to age-matched control children.
"Together [the] findings suggest that nodding syndrome is an epidemic epilepsy frequently associated with encephalopathy," James Sejvar, from the Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, USA, and colleagues write. "The cognitive impairment could be a result of ongoing epilepsy, or might be a related feature stemming from a common pathophysiology."
The collaboration between the CDC and the Ugandan Ministry of Health found that the condition exhibited several electrographic and clinical seizure types - atonic, tonic-clonic, and atypical absence - that had both focal and generalized onset.
Cold beverages and cold weather were observed to trigger head nodding, which adds to a previously noted elicitor - hot food.
Most magnetic resonance imaging scans exhibited generalized cerebral and cerebellar atrophy while focal or white matter signal abnormalities were not observed, excluding any inflammatory causes. These findings along with stable cerebrospinal fluid protein levels suggested that nodding syndrome is a separate epileptic disorder that is not an encephalitic process.
Altogether, the authors conclude that "the unique clinical and electrographic features of nodding syndrome, the high prevalence of the illness, and the apparent geographic clustering of such stereotyped phenomena make nodding syndrome a distinctive new disorder."
The authors note that the study's 8-month follow up failed to assess the full natural history of nodding syndrome's fatality trends and current emergence as well as its clustering properties.
In an accompanying commentary, Helen Cross, from UCL Institute of Child Health in London, UK, questions the theory that nodding disease is caused by a parasitic disease, onchocerciasis, which is tied to epilepsy. Because of the progressive neurologic and systematic deterioration that is apparent in nodding disease, she suggests "epilepsy is a manifestation rather than an epileptic encephalopathy."
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