Recently, Neary and colleagues (30) have drawn attention to a group of patients with non-Alzheimer's dementia who typically present with changes of personality and social conduct and with atypical Pick's changes in the brain. They note that this form of dementia may be more common than previously thought.
Another form of dementia that primarily affects frontal lobe function is that of normal pressure hydrocephalus. This may be related to several underlying causes, including cerebral trauma, previous meningitis, neoplasia, or subarachnoid hemorrhage, or it may occur idiopathically. Essentially, there is a communicating hydrocephalus with failure of absorption of cerebrospinal fluid (CSF) via the sagittal sinus through blockage, the CSF being unable to reach the convexity of the brain or be absorbed through the arachnoid villi. The characteristic clinical features of normal pressure hydrocephalus include gait disturbance and incontinence, with normal CSF pressure. The dementia is of recent onset and has characteristics of a subcortical dementia with psychomotor slowing and dilapidation of cognitive performance, in contrast to more discrete memory abnormalities that may herald the onset of Alzheimer's disease. Patients lose initiative and become apathetic; in some cases the presentation may resemble an affective disorder. In reality the clinical picture can be varied, but frontal lobe signs are a common feature and, especially when combined with incontinence and ataxia, should alert the physician to the possibility of this diagnosis.
Other causes of dementia that may present with an apparently focalized frontal picture include tumors, especially meningiomas, and rare conditions such as Kufs' disease and corticobasal degeneration.
DETECTION OF FRONTAL LOBE DAMAGE
Detection of frontal lobe damage can be difficult, especially if only traditional methods of neurologic testing are carried out. Indeed, this point cannot be overemphasized, since it reflects one of the main differences between traditional neurologic syndromes, which affect only elements of a person's behavior - for example, paralysis following destruction of the contralateral motor cortex -and limbic system disorders generally. In the latter it is the whole of the patient's motoric and psychic life that is influenced, and the behavior disturbance itself reflects the pathologic state. Often, changes can be discerned only with reference to the previous personality and behavior of that patient, and not with regard to standardized and validated behavioral norms based on population studies. A further complication is that these abnormal behaviors may fluctuate from one testing occasion to another. Therefore the standard neurologic examination will often be normal, as may the results of psychological tests such as the Wechsler Adult Intelligence Scale. Special techniques are required to examine frontal lobe function, and care finding out how the patient now behaves and how this compares with his premorbid performance.
Orbitofrontal lesions may be associated with anosmia, and the more the lesions extend posteriorly, the more neurologic signs such as aphasia (with dominant lesions), paralysis, grasp reflexes, and oculomotor abnormalities become apparent. Of the various tasks that can be used clinically to detect frontal pathologic conditions, those given in Table 4 are of value. However, not all patients with frontal damage show abnormalities on testing, and not all tests are found to be abnormal in frontal lobe pathologic states exclusively.
Table 4. Some Useful Tests at Frontal Lobe Function
Abstract thinking (if I have 18 books and two bookshelves, and I want twice as many books on one shelf as the other. how many books on each shelf?)
Proverb and metaphor interpretation
Wisconsin Card Sorting Test
Other sorting tasks
Hand position test (three-step hand sequence)
Copying tasks (multiple loops)
Rhythm tapping tasks
Cognitive tasks include the word fluency test, in which a patient is asked to generate, in 1 minute, as many words as possible beginning with a given letter. (The normal is around 15.)
Proverb or metaphor interpretation can be remarkably concrete.
Problem-solving, for example carry-over additions and subtractions, can be tested by a simple question (see Table 4). Patients with frontal lobe abnormalities often find serial sevens difficult to perform.
Laboratory-based tests of abstract reasoning include the Wisconsin Card Sort Test (WCST) and other object-sorting tasks. The subject must arrange a variety of objects into groups depending on one common abstract property, for example color. In the WCST, the patient is given a pack of cards with symbols on them that differ in form, color, and number. Four stimulus cards are available, and the patient has to place each response card in front of one of the four stimulus cards. The tester tells the patient if he is right or wrong, and the patient has to use that information to place the next card in front of the next stimulus card. The sorting is done arbitrarily into color, form, or number, and the patient's task is to shift the set from one type of stimulus response to another based on the information provided. Frontal patients cannot overcome previously established responses, and show a high frequency of preseverative errors. These deficits are more likely with lateral lesions of the dominant hemisphere.