Cognition is the mental action or process of acquiring knowledge and understanding through thought, experience, and the senses. It encompasses various aspects of high-level intellectual functions and processes such as attention, memory, knowledge, decision-making, planning, reasoning, judgment, perception comprehension, language, and visuospatial function. Cognitive processes use existing knowledge and generate new knowledge.

“Cognitive deficit” is an inclusive term used to describe the impairment of different domains of cognition. Cognitive deficit is not limited to any particular disease or condition but may be one of the manifestations of someone’s underlying condition. It is also used interchangeably with “cognitive impairment.” It might be a short-term condition or a progressive and permanent entity.

On the other hand, cognitive disorders are a bigger entity, which is a part of neurocognitive disorders (DSM-5). Cognitive disorders are defined as any disorder that significantly impairs the cognitive functions of an individual to the point where normal functioning in society is impossible without treatment. Alzheimer disease is the most well-known condition associated with cognitive impairment.

Etiology

Cognitive deficits may be from birth or caused later by environmental factors such as brain injury, mental illness, neurological disorders. Not every elderly will have a cognitive deficit, but the cognitive deficit is more common in the elderly. 

Some of the early causes of cognitive deficit include chromosome abnormalities/genetic syndromes, prenatal drug exposure, malnutrition, poisoning due to lead or other heavy metals,  neonatal jaundice, hypoglycemia, hypothyroidism, prematurity, hypoxia, trauma, or child abuse.

In childhood or adolescence, Cognitive deficit may develop as a result of many conditions. Some examples include side effects of cancer therapy, heavy metal poisoning, malnutrition, metabolic conditions, autism, and immune conditions like systemic lupus erythematosus.

With increasing age, conditions such as stroke, delirium, dementia, depression, schizophrenia, chronic alcohol use, substance abuse, brain tumors, vitamin deficiencies, hormonal imbalances, and some chronic diseases may cause a cognitive deficit. Brain pathologies like Alzheimer disease, Parkinson disease, Lewy body dementia, Huntington disease, HIV dementia, prion disease manifest with cognitive deficits. Drugs like sedatives, tranquilizers, anticholinergic, glucocorticoids are also associated with cognitive deficits. Head injury and infection of the brain or meninges can cause cognitive deficits at any age.

Epidemiology

The frequency of cognitive deficit due to various causes is difficult to predict and is not well established. However, increasing age is the most important factor for cognitive impairment. Alzheimer disease is the most well-known condition associated with cognitive impairment. Approximately 5.5 million people are affected by Alzheimer disease in the US, and the worldwide prevalence is estimated to be more than 24 million.

The prevalence and incidence of Alzheimer among African American populations were approximate twice those among European Americans. The incidence of dementia is predicted to double every 10 years after 60 years of age. Age-specific incidence of Alzheimer disease increases significantly from less than 1% per year before the age of 65 years to 6% per year after the age of 85 years.

Pathophysiology

The general pathology of cognitive decline/deficits is damage to neuronal tissue.  This includes damage to the grey matter, which comprises the cortex and the thalamus and basal ganglia, and the white matter, which comprises the coverings of the axons of the connections between grey matter areas. The damage to certain areas is responsible for certain deficits. For instance, damage to the parietal lobe can cause the inability to dress or visuospatial function.  Damage to the frontal lobe systems can cause deficits in planning, and abstract understanding and damage to the temporal lobes cause deficits in language and memory.

The causes of this damage are due to toxicity to neurons from metabolic disorders or heavy metals or other toxins such as toluene or infection or due to ischemic damage due to stroke or hemorrhage or direct injuries such as head injury or cancer or surgery. Damage can also be caused by neurodegenerative processes such as Alzheimer, Parkinson, multiple sclerosis, or Huntington disease.  These illnesses appear to directly damage neuronal tissue through immunologic interaction with abnormal proteins.

Histopathology

Most of the dementias are confirmed by finding abnormal proteins in brain sectioning. Alzheimer is defined by amyloid and Tau inclusions in the brain tissue, Parkinson and Lewy body dementia are supported by Lewy bodies and frontal dementias by Tau inclusions. Parkinson-like illness is also associated with Synleuclin inclusions. Prion diseases have abnormally folded proteins called prions in the brain tissue.

History and Physical

Cognitive deficit is not an illness in itself but a manifestation of an underlying condition. The patient may notice these changes themselves, or most of the time, it is noticed by the caretakers and friends of the patient. The patients usually have the following:

• Trouble remembering things (frequently asking the same question or repeating the same story again and again )
• Difficulty in learning new things and concentrating
• Vision problems and trouble speaking
• Difficulty recognizing people and places. They often find new places or situations overwhelming.
• Confusion or agitation.
• Mood changes
• Change in their behavior, speech,
• Difficulty even with their usual daily tasks

Cognitive impairment can come and go or wax and wane. Cognitive impairment can be mild, or severe, or anything in between. With mild impairment, there are changes in cognitive functions, but the individual can still do his/her everyday activities. Severe levels of impairment (dementia) can lead to a point where the individual is incapable of living independently because of the inability to plan and carry out regular tasks (Activities of daily living/instrumental activities of daily living) and apply judgment.

Cognitive impairment may accompany different other symptoms, depending on the underlying disorder or condition. Sometimes they may present as emergency cases and may require acute life-saving interventions.

Infective causes may present with fever, rashes, headache, nausea, vomiting, neck stiffness, malaise, seizures, and others.

It may accompany metabolic disorders and present with abdominal pain, nausea, vomiting, tachycardia, bradycardia, fatigue, muscle weakness, shortness of breath, excess thirst, urinary problems, and even loss of consciousness. 

Cognitive deficits may accompany symptoms of other problems, such as head injury, stroke, or dementia. The patient might present with behavioral or personality changes, loss of consciousness, vision changes, imbalance, severe headaches, seizures, sleep pattern changes, numbness, weakness, and paralysis. 

Cognitive disorder includes delirium and mild and major neurocognitive disorder, which may present as follows:

• Delirium develops very rapidly and over a short period of time. It is mainly characterized by disturbances in cognition. Other manifestations are confusion, disorientation, excitement, and also a change in consciousness. Hallucinations and illusions may be common. It also makes processing new information and situational awareness very difficult. Its onset ranges from minutes to hours and sometimes days. However, it only lasts a few hours to weeks. It can also be accompanied by inattention, mood swings, or abnormal behaviors. There is usually an underlying medical or surgical condition causing it. Delirium during a hospital stay can result in complications and long terms stay.
• Mild and major neurocognitive disorders are commonly associated with the elderly. These disorders develop slowly and are mainly characterized by memory loss in addition to cognitive impairments. There may also be psychosis, agitation, and mood changes. The difference between mild and major neurocognitive disorders is mainly based on the severity of the symptoms. Major neurocognitive disorder(previously known as dementia) is characterized by significant cognitive decline and the development of dependence. The mild neurocognitive disorder is characterized by moderate cognitive decline, and the patient is still independent. To be diagnosed, delirium and other mental disorder should be ruled out. For causes of dementia such as age, which is irreversible, the decline of cognition and memory is lifelong.

Evaluation

The evaluation consists of detailed history from patient and family members (including the onset, duration, symptoms, impact, impact on activities of daily living, and changes from the patient’s previous level of execution and functioning) and clinical assessment of the patient that encompasses a wide range of information collected from physical, neurological, and mental status examinations.

The history gathered from the patient and the accompanying family/friend should be focused on:

• Changes in cognitive functions (onset, course, and examples)
• Change in functional status-Selfcare (cooking,testing,hygiene,finances)
• Physical symptoms (nausea, vomiting, vision, hearing, speech, balance, gait, balance, sensation, and motor functions)
• Psychiatric symptoms (mood changes, behavioral and personality changes) 
• Current medication, if any

Treatment / Management

Treatment of cognitive deficits depends on what actually is causing impairment. If it is caused by an illness or a condition, then it is likely to recover after the treatment. Infections and metabolic syndromes, depression, thyroid disorders, Medication effects are some curable causes of cognitive decline. For cognitive disorders, a detailed assessment and management are required, and the interventions focus mainly on the improvement of quality of life and the limitation of residual defects.

There is no pharmacological treatment for mild cognitive impairment. The management is focused on promoting functional status. Counseling is a very important component of patient management. These individuals are at increased risk for trouble with mobility and recurrent falls. Problems with vision and hearing need to be addressed and corrected. People with sleep apnea may be benefited from continuous positive airway pressure (CPAP). There is no established evidence to conclude that the treatment of depression improves cognitive impairment. There are negative impacts of the use of anticholinergic medications on cognitive function in the elderly. The treatment with antidepressants should be avoided, especially the ones with amitriptyline, nortriptyline, and paroxetine (ones with significant anticholinergic properties). A trial of withdrawing, managing, and simplifying medications in older adults may lead to an effective improvement in cognitive function.

For the treatment of delirium, the cause must be established first. Medication such as antipsychotics or benzodiazepines (BZDs) can help reduce the symptoms in some cases. For alcohol abuse or malnourished cases, vitamin B supplements are recommended. Some extreme cases also require life support. Ginkgo biloba is a popular herbal supplement that is thought to improve cognition and memory. However, it has failed to prevent cognitive decline in those with mild cognitive impairment or normal cognition in randomized control trials.

Physical activity, cognitive training and exercises, proper sleep, and relaxation techniques can help cognitive health. Mediterranean diet may help people with cognitive impairment. Occupational therapy focuses on teaching different patient strategies to minimize the effect of cognitive impairment on daily life. Environmental approaches, such as reducing noise around the patient, help the patient focus on tasks, and reduce distraction, confusion, and frustration. They are making sure that the patient is around familiar objects and surrounding helps. Psychotherapy and psychosocial support for patients and families have evidence of better outcomes in clear understanding and proper management of the disorder and therefore maintaining a better quality of life for everyone involved.

Differential Diagnosis

Cognitive deficit is not an illness in itself but a manifestation of an underlying condition. Some disease conditions associated with cognitive deficits are:

• Delerium
• Alzheimer disease
• Huntington disease
• Stroke
• Developmental disorders (Down syndrome)
• Head injury
• Multiple sclerosis
• Parkinson disease
• Lewy body dementia
• Meningitis
• Acquired immune deficiency syndrome
• Alcohol, drugs, toxins
• Wernicke Korsakoff syndrome

Prognosis

The prognosis of cognitive deficits depends upon the underlying cause. There are many causes like medication, depression, thyroid disorders, infections, which are correctable. Whereas conditions like Alzheimer disease cannot be reversed, and only the progression can be slowed. Many causes of cognitive deficits are acute life-threatening conditions, and without proper medical or surgical management can result in a great deal of morbidity and mortality. For patients diagnosed with Alzheimer disease, the average life expectancy for a person age 65 years or older is about 4 to 8 years. Some individuals with Alzheimer disease even may live up to 20 years after the first signs of disease.

In some instances, cognitive deficits may be a symptom of an underlying serious or life-threatening condition that can be life-threatening. These include:

• Brain tumor
• Stroke
• Encephalitis
• Meningitis
• Traumatic head injury 
• Heatstroke or profound dehydration
• Kidney failure
• Sepsis
• Spinal cord injury or tumor

Complications

A cognitive deficit can be coexisting with a variety of serious diseases and conditions. Therefore the failure to timely seek treatment can result in serious complications and even permanent damage. Once the underlying condition is diagnosed, it is important to follow a proper treatment plan to reduce the risk of potential complications, which may include:

• Developmental delays and failure to thrive
• Learning disabilities
• Speech and hearing defects
• Paresis/paralysis
• Permanent cognitive impairment
• Permanent sensory loss
• Physical disabilities
• Personality changes
• Permanent loss of memory
• Loss of independence
• Falls/injuries
• Coma