Idiopathic normal pressure hydrocephalus, or iNPH, affects the walking ability and mobility of the elderly, with additional symptoms that include urinary urgency, incontinence and in some cases mild cognitive impairment or dementia.
Usually, iNPH goes undiagnosed because its symptoms mimic those of other neurological disorders. In particular, doctors confuse it with an incurable form of dementia known as progressive supranuclear palsy, or PSP.
A series of experiments suggest that a simple walking exam can accurately distinguish iNPH from PSP up to 97% of the time, according to the German researchers.
"Worldwide, the portion of the elderly is growing. This will inevitably go along with an increased total number of dementias and gait disorders," said Dr. Charlotte Selge
, lead author of the study and an assistant physician in the Neurological Clinic Grosshadern at Ludwig Maximilian University in Munich.
If older patients are routinely given walking tests, those with a reversible form of iNPH might be identified and receive treatment early enough to overcome their illness. Past studies
show that shunt surgery to divert cerebrospinal fluid effectively cures many patients.
Walking the walk
For the study, Selge and her colleagues analyzed and compared the "gaits" or walking styles of 38 patients diagnosed with PSP, 27 patients diagnosed with iNPH and 38 healthy volunteers. Though most participants hovered around age 70, none of them needed a cane or aid to walk 30 feet or more.
A pressure-sensitive carpet helped the researchers examine each participant's gait under five separate test conditions. In the first three tests, participants walked at their preferred speed, next at a slow speed and then at their fastest speed. In the fourth test, participants walked while counting backward. Finally, in the fifth test, participants walked while carrying a tray.
What did the researchers see?
Generally, patients with PSP tend to fling their legs forward while walking, and when turning, they do so abruptly and uncontrollably. By contrast, iNPH patients appear as if their feet are glued to the ground, and some swing their arms in an exaggerated way. Patients with PSP fall more frequently than those with iNPH, but in both disorders, hitting the ground is believed to be related to motor and cognitive impairments.
Though both groups of patients had generally poor gait compared with healthy volunteers, those with iNPH had worse stride, moving more broadly from side to side.
However, walking speeds in patients with PSP slowed by 34% when they walked and counted backward, compared with 17% slower speed for those with iNPH.
When carrying a tray while walking, people with PSP walked slower and their overall gait worsened compared with healthy volunteers and patients with iNPH. In fact, the patients with iNPH showed improved gait while carrying a tray.
Having defined the differences in walking styles for these two conditions, Selge and her colleagues accurately diagnosed those with PSP and those with iNPH 82% of the time based only on gait. And, when they added in the scores from the dual-task tests, the researchers' diagnostic accuracy increased to 97%.
"iNPH is one of the rare causes of a potentially treatable and reversible dementia syndrome and gait disorder, but it is still underdiagnosed," Selge said. The exact number of people with iNPH worldwide is not known, but a Swedish study
suggests that prevalence is about 0.2% in people between ages 70 and 79 and nearly 6% in those older than 80.
She explained that walking symptoms alone are "usually not sufficient to diagnose iNPH and recommend shunt surgery" since each of the symptoms can have multiple causes.
For this reason, she said, "diagnostic tests are required ... to exclude other conditions and to identify patients likely to respond to shunt surgery."
Dr. G. Peter Gliebus
, an assistant professor of neurology and director of the Cognitive Disorders Center at Drexel University College of Medicine, said the strength of the new study is that "it provided an objective evaluation of gait in both disorders."
Gliebus, who was not involved in the research, also noted that the researchers "evaluated changes in gait under different conditions, such as introducing dual tasks."
This was another positive result of the study and should allow doctors to make a more accurate comparison between the two conditions.
"Patients who are diagnosed early into the disease have a higher likelihood of improvement from a shunting procedure," said Gliebus, who is currently researching iNPH.
"Both conditions may present with impaired gait and postural instability," he said. "With time, the gait impairment pattern becomes more specific to these conditions."
Dr. Carol F. Lippa, director of the Cognitive Disorders and Comprehensive Alzheimer's Disease Center at Thomas Jefferson University Hospital in Philadelphia, said that a weakness of the study is the lack of autopsy confirmation for each patient's diagnosis.
Still, the "low-tech, inexpensive, and relatively straightforward measures" of diagnosis presented in the new study are "refreshing," said Lippa, who was not involved in the research. "Additional studies will determine whether this simple testing will be useful in diagnosing patients with both cognition and gait problems."