Introduction   

Ideomotor limb apraxia is the disturbance of planning and of execution of motor activity,which is not caused by a dysfunction of the motor or sensory nervous system. Apraxia is a diagnostic criterion in dementialike Alzheimer's disease. However, this symptom may also occur in dementia with subcortical lesions like Huntington's disease (HD), a hereditary, devastating neurodegenerative disease leading to neurological and psychiatric dysfunction. The aim of our study is to determine the correlation between the occurrence of ideomotor limb apraxia and neuropsychological deficits in HD.

Methods   

To assess the correlation between apraxia and neuropsychological abilities in HD, 41 patients with HD and 33 age- and sex-matched controls were examined. The De Renzi test for apraxia and an apraxia test battery containing tests of i) imitation of meaningless gestures of hands, ii) imitation of meaningless gestures of fingers, iii) performance of meaningful gestures on demand, and iv) pantomime of tool use were used to assess apraxia. Moreover, neuropsychological function was rated by the Mini Mental State Examination (MMSE), the Rey Complex Figure Memory Test, the Trail Making Test A and B, the California Verbal Learning Test (German version), the Stroop Color and Word Test, the Controlled Oral Word Association Test, and the Mehrfachwahl- Wortschatz-Intelligenztest for measuring verbal intelligence. Motor function was assessed in all HD patients by the Unified HD Rating Scale (UHDRS), rating oculomotor and orolingual function, fine motor tasks, parkinsonism, dystonia, chorea and statics and gait.

Results   

Apraxic HD patients showed worse results than non-apraxic HD patients in three items of the Rey Complex Figure Memory Test (Organisation, short-term and longterm memory), but not in other assessed neuropsychological tests. In assessment of meaningful gestures on demand 39.3% of HD patients were apraxic, in assessment of pantomime of tool use 67.9% of HD patients showed apraxia. Patients with HD showed highly significant worse results than controls in the De Renzi test, in hands' and fingers' imitation, in performance of gestures on demand, in pantomime of tool use and every neuropsychological test except for the test measuring verbal intelligence. Apraxic HD patients showed worse results than non-apraxic HD patients in the UHDRS total motor score and the score for oculomotor function.

Conclusion   

This is the largest study on apraxia in HD. Ideomotor limb apraxia is a common sign in HD patients, occurring in a high percentage. In contrast to the opinion of several authors, occurrence of apraxia in HD is independent from neuropsychological decline and the severity of most neurological symptoms.