Cognitive Impairment in Dementia: Symptoms and Diagnosis

Cognitive Impairment in Dementia

This article discusses the most relevant aspects of some of the more frequent cognitive symptoms of dementia. We review the superior functions that are altered during the evolutionary process of dementia, taking Alzheimer’s disease with amnesic syndrome-aphasic-apraxic-agnostic as a paradigm. Then, we analyze the clinical differences between the most common dementias: cortical and subcortical.

Introduction

A few years ago, the concept of dementia was always related to brain aging, being popularly synonymous with senile dementia. At present, taking into account increased life expectancy in developed countries and the prevalence of primary degenerative dementia, particularly Alzheimer’s disease in elderly populations, this parallel is set almost unilaterally with the latter process.

Dementia is a syndrome related to various etiologies, characterized by acquired cognitive decline, variably extensive, affecting several areas of mental performance, altering the patient’s socio-occupational functioning.

This general concept has resulted in numerous operational criteria. Among others, the most used are those of the American Psychiatric Association, DSM-IV (Table I) and the International Classification of Diseases of the World Health Organization ICD-10 (Table II). These criteria are well known and widely used, but both have been criticized. The principal one refers to the main condition for the existence and objectification of a memory disorder, but while typical of Alzheimer’s disease, it may be of little importance in other brain processes included in the syndrome of dementia, as is frontotemporal degeneration or vascular dementia. Moreover, behavioral disorders or mental problems in the organization of tasks can be an almost paradigmatic manifestation of some dementias, not being viewed as such in the above criteria that refer to the concept of dementia. Similarly, establishing a minimum evolution of six months (ICD-10 criteria) may be helpful for some, but a significant number of secondary dementias are developed in a shorter period, being of extraordinary importance their early diagnosis (e.g., subdural hematoma, Creutzfeldt-Jakob disease). Therefore, since the group of behavioral neurology and dementia of the Spanish Society of Neurology, an updated proposal to the previously mentioned criteria was made (Table III).

Whereas in recent decades, changes have been various, both social and health care related to persons with dementia (PwD). In the 1970s, when an elderly subject had any of these signs, or in isolation a major disruption of memory, the diagnosis of senile dementia was fast, of inexorably towards disability prognosis and that little attention was paid to health beyond a certain dedication diagnosis by specialists in neurology or psychiatry.

In the last fifteen years, we have attended a welcome change of “consideration” related both to the cognitive process itself as symptoms “noncognitive,” also described as psychological and behavioral (SPDC), as well as the social aspects focusing on the caregiver who suffers the disease progression (Table IV). Not only that, as at present, most efforts are aimed at identifying population groups at risk, with the optimism of achieving a therapeutic arsenal to prevent the occurrence, or at least delay the development of dementia syndrome in any form, but more particularly Alzheimer’s disease.

At present, the diagnosis of dementia is based on different aspects, holistically, taking into account the clinical symptoms in the broadest sense (cognitive, behavioral, and functional), and the impact it has on the social environment (especially the primary caregiver) of the patient (Table V).

The content of this article, limited by its size, includes the most relevant aspects of some of the cognitive symptoms of dementia more frequently.

Although summarized and schematic, it is necessary to recall the most common causes of dementia, primary and secondary (Table VIa, Table VIb) – as well as anatomically impaired cortical and subcortical (Table VII) – and the clinical characteristics according to these conditions. Currently, the previous classifications related to the age of onset or prognosis are invalidated.

Alzheimer’s disease (AD) is the most common primary degenerative dementia, with a prevalence of between 6-8% in the population over 65 years, doubling every five years from this age, reaching 30% of the elderly over 85. However, Lewy body dementia, dementia in Parkinson’s disease, and vascular dementia supplement in elderly subjects, although with slightly lower prevalence, etiological volume of dementia related to different abnormal protein deposits (amyloid, tau, synuclein) (Figure 1).

It is obvious that the extension of this article does not allow us to go into details related to mild cognitive impairment, or the complete description of the symptoms of the different dementias. There is now an array of literature that allows further information.

Cognitive Clinical Features of Dementia

The complexity of the issue requires a prior reminder of some of the higher functions that are altered during the evolutionary process of dementia. Among them, the paradigm is Alzheimer’s disease with the amnesic syndrome-aphasic-apraxic-agnostic. Then we analyze the clinical differences between the most common dementias.

Alterations in Memory: Amnesia

Memory impairment is one of the main clinical features of dementia, and its study has been the main objective of experimental research. Memory is not a unitary process mediated by a single neuroanatomical system. It seems that there are several subtypes of memory that differ from each other in their modes of action, types of information processing, and the anatomical substrates that support them. Although these memory subsystems interact, they are relatively independent and may be differentially altered by the disease that caused it.

Our brains store a large amount of information and past experiences. The learning process includes recording information, storage, and subsequent retrieval.

In an attempt to “organize” knowledge related to memory, Figure 2 summarizes the “travel” from the mental ability to pay attention (fully linked to the parallel record of information) to the conceptualization of the different subtypes of memory.

Logging information is the ability for immediate recall of finished learning it, and lasts only a few seconds. It can be considered before the memory or is the start of short-term memory.

Amnesic processes follow a temporal sequence: the terms of immediate memory, short-term memory, and primary memory refer to the knowledge of what just happened, or what has been learned a few seconds ago and is immediately recalled. Short-term memory is before the consolidation of long-term memory. Short-term memory is temporary, lasting a few seconds to a few minutes. Its information may be used “immediately” in making decisions or pass to long-term memory.

Short-term memory has limited capacity and can easily become saturated, while there are no obvious limits on the storage of long-term memory.

In recent years, the concept of short-term memory has expanded with working memory, which is a broader concept for temporary storage and limited, allowing the possibility of keeping various kinds of information and requires different brain areas for temporary storage and manipulation of information.

The terms of long-term memory and semantic memory are applied to memory processes related to the recall of information that is stored after a few seconds and includes both the material covered in the very recent past as very remote.

The term recent memory is used clinically as a synonym of information acquired in the recent past, while remote memory applies to the knowledge of personal and social events that occurred in the past tense, even decades ago.

There are actually two types of long-term memory: procedural and declarative. The first relates to the memory of how to run a set of skills (driving, swimming, etc.). With the initial practice and achievement of motor skills, memory becomes an implicit procedure, i.e., performed without clear awareness of it (without realizing).

Declarative memory involves facts and data, both verbal and nonverbal (pictures, sounds, etc.), to different skills and procedures. It is explicit, in that it must be remembered in a state of ‘clear conscience’. In turn, in declarative memory, we can consider episodic memory and semantic memory. The first refers to both the storage and the memory of autobiographical events that depend on temporal or spatial contextual supports for recovery (memory of sequential events). The information in semantic memory is stored in a free of context, without references that characterize the episodic autobiographical. It refers to general knowledge, which consists of facts and concepts learned that are independent of context to support their recovery.

The box itself amnesia, in which failure of memory encoding and therefore it can not be stored or retrieved, is characteristic of Alzheimer’s disease (AD). It is sometimes also seen in dementia with Lewy bodies and vascular dementia with medial temporal involvement.

The failure of memory retrieval is caused by disruption of frontal-subcortical circuits. In these circumstances, the encoding of memory is intact, and may be recognized with tracks or multiple choices. This type of alteration is typical of frontotemporal dementia, the majority of vascular dementias, Creutzfeldt-Jakob disease, and all subcortical dementias.

Language Disorders: Aphasia

Human communication is established through verbal and nonverbal mechanisms. Facial expression, body position, gestures, and drawings are part of nonverbal language, while letters, words, and phrases are used as rules of grammar, the verbal elements.

In language, consider the semantic and motor components, the first being related to the transmission of the content or meaning, and including the second articulation, the phonemes and morphemes (the union of a set of words), facial expressions, gestures, and writing.

The left frontal lobe is very important with respect to the motor aspects of language, while the left temporal area is to the semantics. Classically associated with left frontal injuries is Broca’s aphasia, and left temporal with Wernicke’s aphasia.

While the dominant hemisphere controls most aspects of language, the right plays an important role by allowing the use of metaphors and mastery of the meaning of abstract verbal communication. This hemisphere acts by integrating functions, which seems necessary to appreciate the whole and establish the meanings that underlie the manifest content of communication.

The assessment of language should cover all aspects related to the concepts described above, and fluency, naming, comprehension, reading, writing, mistakes in the use of words (paraphasias), etc., will guide the characteristics of the language disturbance (aphasia). Table VIII summarizes the differences between the types of aphasia.

In AD, although the beginning is characterized by anomia (difficulty naming objects), it progresses into a transcortical sensory aphasia, reaching echolalia (involuntary repetition of a word or phrase) and palilalia (involuntary repetition of a progressively faster word) in advanced stages.

In frontotemporal degeneration, variants of clinical presentation include: Frontotemporal dementia (FTD), semantic dementia (SD), and nonfluent primary progressive aphasia (PPA). The subject suffers from a lack of inflection with dysprosody (FTD), a semantic anomia progression to Wernicke’s aphasia and mutism (SD), or Broca’s aphasia or transcortical motor type in primary progressive aphasia (PPA).

In Dementia with Lewy bodies (DLB), although clinical semiology neurological (parkinsonism, syncope, fluctuations in vigilance level, alteration in REM sleep behavior) is different from AD, the language disturbance follows a course similar to Alzheimer’s Disease, yet the prevalence extrapyramidal probably difficult to identify these alterations.

Alterations of Gesture: Apraxias

Apraxia is not an elementary motility disorder, but refers to the deliberate execution of certain activities gesture. It describes the change in the execution of a gesture, usually learned, not caused by paresis, loss of sensation, movement disorder, altered muscle tone, coordination, collaboration, understanding, or other cognitive impairment.

The practical implementation is based on two essential components: the conceptual and production. Thus, the conceptual system contains knowledge about the function of objects and tools, while the production system stores the spatial and temporal information necessary for the execution of movements.

Different types of apraxia appear in the evolution of the syndrome of dementia and can be defined include: constructive apraxia as a disruption in constructive activities such as lace pieces, construction, and design, which do not get the achievement of certain forms, despite not having an apraxia simplest movements independently; ideomotor apraxia, in which the subject is able to perform a given set of actions unintentionally be impossible in situations out of context; ideational apraxia, the inability to conceptualize the action plan required to achieve a desired object; apraxia of dressing, to the disintegration of the gestures that electively and tidy up the action of the clothes properly placed, because of an inability to align the body axis to the axis of corresponding garment.

The bilateral parietal impairment (apraxia of dressing) or right posterior parietal (constructional apraxia) in different evolutionary moments of dementia will lead to the corresponding presence of symptoms.

Alterations of Recognition: Agnosia

The term agnosia involves a loss of the ability of the recognition of objects by the senses. Agnosia is a disorder in visual recognition of objects by sight, in the absence of a language disorder or sensory function. So, too, differ agnosias tactile and auditory. In addition, other modalities may differ according to the type of stimulus such as colors, objects, or faces. Subjects with agnosia usually have more than one type of stimulus, and more than one modality.

The most common are agnosias of objects and faces. There are two main disorders of object recognition, one that affects the perceptual stage of the analysis of objects, and another in which it alters the process by which meaning is assigned to visual stimuli (Figure 3).

Although not the most initial symptom in AD, agnosias of different modalities are variably present in the evolution of one of the most common degenerative dementia. Special mention should be made of visual gnosic disturbances in degenerative focal (posterior cortical atrophy).

Differences in Clinical Cognitive Dementia

Cortical Dementia

The cortex, as an essential biological substrate of cognitive functions, has conditioned the name of those cortical dementias in which cognitive impairment mainly affects language, memory, praxis, recognition, and abstraction. In this line, which attempts to describe the clinical features oriented towards the location, differ in ways temporoparietal cortical dementias, frontotemporal. Also been described as focal, those in which symptoms predominate localized and limited in the cortex (posterior cortical atrophy, progressive apraxia).

The paradigmatic temporoparietal dementia is AD, which forms progressively amnestic syndrome-apraxic-aphasic-agnostic. In contrast, frontotemporal degeneration is characterized by disturbed behavior, lack of motivation, preserving the memory initially (FTD), or a disorder of language (semantic dementia, primary progressive non-fluent aphasia) with initial preservation of other cognitive functions.

Subcortical Dementia

This term refers to a portion to a clinical presentation of dementia semiologically distinguishable from those described in the preceding paragraph, and the topography of the neurobiological alterations.

However, it has modified his previous assertion that classical higher functions related exclusively to the cerebral cortex (hence the terminology of ‘cortical functions), recognizing the role of subcortical structures, and lesions affecting the basal ganglia, internal capsule, or thalamus, may produce equally aphasic syndromes, alterations praxical and disorders.

The clinical difference will be defined by the prevalence of symptoms (parkinsonian syndromes, syndromes engines, etc.) related to the neuroanatomical substrate.

Table IX summarizes the most relevant aspects discussed above.

Although away from the main objective of this article, it is clear that detailed evaluation of cognitive symptoms previously described must be based both on the history, observation, and examination clinic (neurological and psychiatric), and the neuropsychological examination (Table X). Allowing together, not just the possible etiology of dementia but impaired cognitive abilities and preserved. It is these last ones which focus on the therapeutic objective of stimulation programs and/or maintaining cognitive and basic substrate of non-pharmacological treatment of dementia.