Washington: A speech disorder called apraxia can evolve into a neurologic disorder if left untreated, causing difficulty with eye movement, use of limbs, and

walking that worsens as time passes, scientists say.

Some patients eventually become mute from primary progressive apraxia of speech, a disorder related to degenerative neurologic disease. Because patients and even many medical professionals do not recognise apraxia of speech, treatment typically is sought in later stages of the disease, said Keith Josephs, a

neurologist at Mayo Clinic in US.

As apraxia progresses, it frequently is misdiagnosed as Alzheimer's disease or amyotrophic lateral sclerosis. Apraxia of speech even has been diagnosed as mental illness. "Because it first presents as 'just' a speech problem, some people are told, 'This is in your head'," Josephs said.

When it is caused by a stroke, apraxia of speech typically does not worsen and may get better over time. However, apraxia of speech often is ignored as a distinct entity that can evolve into a neurologic disorder, causing difficulty with eye movement, using the limbs, walking and falling that worsens as time passes.

"It is a devastating disease, in some sense worse than Alzheimer's disease, which typically spares balance and walking until very late in the disease course," said Josephs. "It may start with the person simply not being able to pronounce a few words. Six years after that, they are in a diaper, can't speak, can't walk and are drooling," said Josephs.

The benefit to getting an early and correct diagnosis is that people can receive appropriate therapy. While speech therapy does not reverse or halt the

progression of apraxia, it can develop compensations for producing better sounds.

People with apraxia of speech also can use computers or texting for alternate means of communicating. Both the value and complexities of speech often are underappreciated. Speech is a complex brain-body achievement, researchers

said. It first requires selection of appropriate words, organising them into a coherent message.

This message activates 100 muscles between the lungs and lips to produce at least 14 distinct sounds per second that can be comprehended by a listener.

A problem with speech programming - directing the muscles and structures that move - is apraxia.

The findings were published in the journals Brain, Neurology, the American Journal of Alzheimer's Disease and Other Dementias, and the Journal of Neurology.