Introduction

The cognitive disorder in HD is considered a "subcortical" syndrome and usually lacks features such as aphasia, amnesia, or agnosia that are associated with dementia of the Aizheimer's type.

The most prominent cognitive impairments in HD involve the so-called "executive functions" abilities such as organization, regulation and perception. These fundamental abilities can affect performance in many cognitive areas, including speed, reasoning, planning, judgment, decision making, emotional engagement, perseveration, impulse control, temper control, perception, awareness, attention, language, learning, memory and timing.

Several studies have suggested that cognitive and behavioral impairments are greater sources of impaired functioning than the movement disorder in persons with HD, both in the work place and at home. In addition, family members most often report that placement outside the home is initiated because of cognitive and behavioral deterioration rather than motor symptoms.

This chapter provides an overview of cognitive impairments and the related behavior problems that typically accompany HD. In addition, compensation and adaptation strategies are provided, which physicians may recommend to patients, families and other professionals.

The Progression of Cognitive Impairments

Although performance in IQ tests often remains within the normal range in the early stages of the disease, cognitive deficits are evident in speed of processing, cognitive flexibility (or the ability to shift topics readily) and the organization of complex information.

The most sensitive indicator of early HD on the Mini-Mental State Examination is serial sevens (the ability to subtract 7 from 100 serially) and the most sensitive subscale on the Mattis Dementia Rating Scale is initiation (the ability to begin and maintain verbal and motor behaviors).

There exist few longitudinal studies of the cognitive decline in HD. Based upon the information available, speed, organization, and initiation of behavior are impaired in early HD, constructional impairments worsen in mid-stage HD, and some abilities remain relatively spared (memory, language comprehension) even in the later stages of the disease.

Clinically, as the disease progresses, the severity of cognitive impairments increases and patients are often unable to speak or communicate their views in late stages.

Disorganization

Difficulties in planning, organization, sequencing and prioritizing can affect responsibilities at home and at work. Daily tasks, such as attempts to follow a recipe, to maintain a daily planner, to complete a list of household errands, to develop a meeting agenda, or to apply for social security benefits, become daunting.

Many early-stage HD patients complain of problems with organization and report that they just "can't get things done." There are several ways to compensate for poor organization, which can be instituted early in the disease.

Routines should be established at work or in the home so that the environment can provide structure and organization. Activities should be organized so that each day is

basically the same. For example, 7:00 shower, 7:30 breakfast, 8:00 take bus to work, 8:30 check mail, 9:30 dictate letters, 10:00 coffee, 10:30 staff meeting, 12:00 lunch, 1:00 return phone calls, 2:30 review accounting, 4:00 open meeting to schedule with customers, 5:00 take bus home, 6:00 dinner, 7:00 family time with kids, 8:30 time with spouse, 9:30 read, 10:00 lights out.

A central location could be established for posting a daily schedule. Persons who never before used daily planners or computer calendars may need to start. A centralized message center can be used to make lists and organize tasks to be accomplished each day. Additional strategies for dealing with poor organization are offered in Table 6.

Lack of Initiation

Some family members complain that the person with HD "just sits around all day and won't do anything." Regulation of behavior involves getting started, maintaining the desired behavior and stopping unwanted behaviors.

The initiation, or starting of an activity, conversation or behavior is often compromised in HD.  A lack of initiation is often misinterpreted as laziness, apathy or lack of interest, and may be a reason for poor performance at work.

Once started, persons with HD may be able to execute the behaviors adequately (i.e., compute taxes, calculate sales, administrate employees, teach school), but may be unable to organize and initiate the behaviors at the appropriate time.

External initiation often helps the person with HD remain active and participate in both social and work activities. Keeping a daily routine can minimize the need for internal initiation. Maintaining the desired behavior is usually less of a problem for persons with HD. If this aspect of regulation is impaired, however, the HD patient may be unable to regulate ongoing behaviors in an appropriate manner.

Perseveration

Perseveration, or being fixed on a specific thought or action, can occur when behaviors are inadequately regulated by the brain. Spouses often report that patients become behaviorally rigid, and tend to get stuck on an idea or task. Established routines and gentle reminders of changing tasks can help avoid problems.

An activity that is atypical for the established routine will be particularly stressful and challenging for the person with HD. For instance, travel out of town, or a visit to the doctor or dentist, may disrupt a safe routine. When shifting to a new task, help prepare the person with HD and allow plenty of time for him to adapt to the new idea. There is a delicate balance of how much preparation is needed. Telling of a change in plans too early can cause increased anxiety. Typically, inform the HD patient only one day prior to an event or a few hours before. Allow plenty of time and frequent gentle cues to allow the shift to take place.

Impulsivity

Some persons with HD experience difficulties with impulse control and may develop problem behaviors such as irritability, temper outbursts, sexual promiscuity and acting without thinking. Some degree of impulsivity and dysregulation of behaviors is quite common in HD.

Some strategies to help family members and caregivers cope with impulsivity are addressed below.