Sensory and Perceptual Alterations

Etiology

The cause of sensory-perceptual alteration depends on the underlying condition and risk factors. Factors that may increase the risk of sensory perceptual alterations include:

Psychiatric Conditions

Autism spectrum disorder (ASD): Alterations in sensory-dedicated neural circuits, including neuro-molecular and anatomical changes in primary sensory regions of the brain, are responsible for autism-associated sensory symptoms. GABAergic (gamma-aminobutyric acid) signaling is often affected and responsible for these alterations.[4]

Attention deficit hyperactivity disorder (ADHD): The inability to inhibit irrelevant sensory extraneous stimuli leads to sensory overload in ADHD. This occurs due to impaired information processing and faulty perceptual capacity. Individuals with ADHD have a reduced ability to filter intrusive sensory, motor, and/or cognitive information.[5]

Schizophrenia: Altered sensory processing and perceptual inference are responsible for the positive symptoms of schizophrenia.[6][7] Aberrant neurotransmitter signaling in the sensory pathway and abnormal cortical plasticity mechanisms are implicated in the pathology of schizophrenia.[8] One of the core features of both schizophrenia and ASD are dysfunctional face emotion recognition and motion processing.[9]

Sensory processing disorder (SPD): SPD is a neurological condition in children when the brain is unable to process incoming information in an accurate and organized manner resulting in inaccurate processing and judgment of sensory information. Children can experience difficulty with regulating emotions, problems in attention, and adapting responses.[10]

Sleep Disorders 

Altered sleep or sleep deprivation can cause delirium leading to sensory and perceptual alterations. The decrease in rapid eye movement (REM) sleep has been ascertained as a possible factor that can cause delirium.[11]

Delirium in Intensive Care 

Critically ill patients in the intensive care unit (ICU) are at increased risk of developing delirium. Sensory and altered perceptions can occur due to host factors, acute illness, and environmental factors. Environmental and iatrogenic factors include sleep deprivation, sensory deprivation, immobilization, and social isolation.[3] Lack of quality and adequate sleep are important risk factors for the development of delirium in patients admitted to the ICU. Such changes negatively affect the quality of care provided to the patients.[12]  

Causes of disturbed sleep in the ICU may be due to:[13][14]

• Mechanical ventilation and medication (benzodiazepines used to treat delirium can also adversely contribute to delirium particularly in elderly patients)[3]
• Continuous exposure to light which will disrupt the circadian rhythm
• Noise exposure: sound from equipment, alarms, conversations amongst healthcare staff or patients 
• Patient care activities: vital signs, nursing procedures, imaging, lab draws

Prolonged or frequent sleep deprivation can lead to:[13] 

• Delirium: due to impaired cognitive function[14]
• Prolonged neurocognitive dysfunction
• A decrease in quality of life
• Impaired immune function

In certain circumstances (for example infection control), it may become necessary to isolate patients. Contact isolation will have a negative impact on a patient's mood, increasing the risk of depression, anxiety, hostility, and fear. Due to the uncertainty of the situation, the patient may feel that they are losing control within social isolation, thus influencing their mood.[15] Elderly patients with neurocognitive disorders under physical isolation are more prone to develop delirium.[16] 

Neurological Disorders

Several of the neurological disorders and syndromes can present with changes in behavior and cognitive function due to altered brain function.[17] These can be due to acute changes related to trauma, metabolic and electrolyte imbalance, medication, infections, or vascular changes. Furthermore, such changes can happen in a slow and insidious fashion due to inherited disorders, neurodegenerative diseases, malignancies, or structural disorders.[17]

Alzheimer's disease: Due to cortical disturbances, sensory visual impairments are a common finding in Alzheimer's disease. This occurs due to the accumulation of neurofibrillary tangles and neuritic plaques in the visual cortical areas leading to cortical degeneration and atrophy. Higher visual abilities are commonly compromised. These include simultanagnosia, problems with visual attention, visual memory, perceiving structure from emotion, object and face perception, visual learning, and reading. Impairment of visual perception in these patients decreases their quality of life and complicates the evaluation of other cognitive deficits.[18][19][20]

Parkinson's disease: The progressive loss of dopaminergic cells in the retina and other areas of the visual system leads to visuoperceptual deficits in patients with Parkinson's disease. This dopamine deficiency in the retina leads to selective spatial-temporal abnormalities in the retinal ganglion cell function. Patients who develop visuoperceptual deficits are at a higher risk for the development of dementia.[18][21]

Seizure disorder: Patients with epilepsy can have perceptual functions with all five senses affected. This results in impaired or occasionally supranormal sensibility. Ictal perceptual experiences are common but interictal function may also be affected. Since epilepsy is a network disease, it can affect neural circuits distant from the seizure focus. This may account for the correlation between sensory modality affected and the underlying epilepsy syndrome. People with temporal lobe epilepsy often experience impairment in olfaction, such as odor discrimination, identification, and recall. Such altered sensation is due to the close association of the olfactory system with the limbic system (which is often implicated in mesial temporal lobe epilepsy). Visual information processing may also be disturbed in occipital lobe epilepsy.[22] 

Visual Dysfunction

Common causes of visual dysfunction in the elderly are:

• Age-related changes in the optics of the eye
• Diabetic retinopathy
• Glaucoma
• Cataract
• Age-related maculopathy
• Visual hallucinations due to Bonnets syndrome 

These dysfunctions lead to impairment in visual acuity, contrast sensitivity, color discrimination, motion perception, peripheral visual field sensitivity, temporal sensitivity, and visual speed processing.[18]

Hearing Problems 

Hearing loss can cause auditory hallucinations, such as Anton's syndrome. 

Electrolyte Imbalance

This can cause an altered sensorium, especially hyponatremia and hypocalcemia, which can induce delirium in elderly patients.[23]

Alcohol or Illicit Drug Use

This can lead to neurocognitive impairments resulting in altered sensory and perceptual alterations.[24][25][26]

Chronic Medical Problems

Liver failure, renal failure, and acquired immunodeficiency syndrome (AIDS) can cause sensory-perception alterations. Other causes can include hospitalized elderly patients, ventilation-perfusion mismatch, polypharmacy, patients with a terminal illness, post-surgical status, or patients with a high fever.[27]

Epidemiology

The prevalence of delirium can range from 3% to 42% during hospital admission.[28] Delirium can be high as 80% in critically ill patients.[29] Such variations depend upon the cause and the host factors. The prevalence of hallucination in the general population has been reported to be as high as 12% and has a significant impact on functional impairment.[30]

Pathophysiology

The mechanism by which sensory and perceptual alteration can occur can be due to a direct insult to the brain or due to aberrant stress responses.[31] Biochemical derangement, due to an increase in dopamine, cortisol,  glutamate, and norepinephrine release, along with decreased cholinergic functions, may cause such changes. Also, changes in increased or decreased serotonin or gamma-aminobutyric acid activity may manifest as different clinical presentations. Age-related changes in neurotransmission and intracellular signaling may also occur and cause alterations. Aberrant stress responses such as acute changes in the environment, trauma, severe illness, and surgery can cause abnormalities and can alter neurotransmitter release leading to sensory and perceptual alterations. Decreased cerebral oxidative metabolism can cause the abnormal release of neurotransmitters leading to cerebral dysfunction. The cellular signaling hypothesis speculates that intraneuronal signal transduction is affected, causing a change in the neurotransmitter production and release leading to altered sensation.

History and Physical

The history will be relevant to the underlying risk factor responsible for sensory-perceptual alteration. Signs and symptoms can occur at a specific time and place when the patient is exposed to a certain environment or trigger, or it can happen instantaneously without any triggers. Furthermore, the signs and symptoms of sensory and perceptual alteration can occur when the patient is exposed to certain stimuli or environmental factors. Such sensory and perceptual disorders would be magnified in an unfamiliar environment, especially when patients are hospitalized in unfamiliar hospital rooms.

Vital signs can be abnormal or normal, depending upon the etiology of the sensory and visual alterations. Patients may not be oriented to time, place, or person. They can be confused, irritable, exhibit a lack of focus and concentration, unable to solve problems or communicate. They may also be suffering from hallucinations (visual, auditory, or tactile). Depending on the altered perception, cranial nerve and sensory examination may be abnormal. The remaining systems examinations can be expected to be normal or variable according to the patient's condition.

Evaluation

Validated assessment tools such as the Confusion Assessment Method for the Intensive Care Unit (CAM-ICU) or the Intensive Care Delirium Screening Checklist (ICDSC) should be used to identify delirium in ICU patients.[29][32] An electrocardiogram, echocardiogram, lab investigations, cerebrospinal fluid (CSF) studies, electroencephalogram, chest X-ray, or computed tomography (CT) scan of the head may be required to ascertain the diagnosis.[33]

Treatment / Management

The main priority is the patients' safety. Such alterations not only increase the stress upon the patient, but patients can be at risk of falls, injuries, and perhaps can be a danger to themselves or to others due to their violent behaviors. The management and interventions depend upon the cause of sensory and perceptual disturbances. Hence careful evaluation is needed to ascertain the cause while assisting the patient and preventing them from any further distress or injuries. 

The patient can be supported to be re-oriented to time, place, and person. This can be done by engaging the patient in a conversation about the current news, weather, or asking them about their hobbies or experiences. They should be frequently monitored and settled in a comfortable environment that is devoid of excessive stimuli (bright lights, noises within the ICU).

Patients who are visually impaired can be provided with corrective lenses and reading material in large print or braille. Conversations should be carried out at the patient's eye level and within their field of vision. The surrounding environment should be organized, and they should be aware of where their items are placed. Patients with hearing deficits should be provided with their hearing devices. To ensure effective communication, the environment should be noise-free. The written form of communication or sign language may be facilitated to aid in communication. 

To treat or prevent ICU delirium, a multicomponent intervention should be adapted. This includes both pharmacological and non-pharmacological interventions.[3] However, the response to pharmacological intervention with antipsychotics is variable.[34] Another review states that the use of pharmacological interventions for the prevention and management of delirium is associated with poor outcomes. Henceforth, pharmacological intervention to manage delirium in the ICU is not recommended.[35] (B2)

Non-pharmacological intervention to prevent and manage delirium in the ICU includes:[3]  (B2)

• The use of earplugs and eye masks 
• Noise control strategies and music therapy
• Bright light therapy
• Cognitively stimulating activities
• Medication review

Providing adequate sleep in terms of length and quality is necessary to prevent sleep deprivation, and thus delirium in patients admitted to the ICU. Improving sleep hygiene has been associated with a decreased risk of delirium.[36] The use of earplugs and eye masks is recommended to reduce noise levels and block out bright light. These non-pharmacological interventions are known to have a positive effect on the quality of sleep of patients admitted to the ICU.[12][13][36] (A1)

Auditory hallucinations due to mental health problems such as schizophrenia, bipolar disorders, post-traumatic stress, and dementia can be assessed by clinical observation or by talking to the patients. The patient may say that they are hearing voices, or the clinician may see the patient talking to themselves. Apart from a full assessment to identify the specific cause, the patient can be managed with medications, cognitive-behavioral therapies, or with a psychotherapist. Visual hallucinations due to mental health problems, sleep disorders, or substance misuse should be managed according to the cause with appropriate medications to treat the cause along with cognitive-behavioral therapies or wit a psychotherapist. Similarly, other hallucinations can affect smell and taste and will need appropriate supportive therapy.

Differential Diagnosis

The following differential diagnosis can be implicated in sensory-perceptual alterations:[33]

• Cognitive impairment
• Stroke
• Polypharmacy
• Anticholinergic drugs
• Psychotropic drugs
• Dehydration or malnutrition
• Multiple comorbidities including liver and renal failure
• Sepsis or due to infectious cause
• Terminal illness
• Metabolic acidosis
• Constipation
• Sleep deprivation
• Depression
• Loneliness with few social contacts
• Transient electrolyte imbalance
• Generalized tonic-clonic seizure
• Vision or hearing impairment

Prognosis

Prognosis depends upon the cause of the sensory and perceptual alterations. The key components in management are early recognition and prevention of any injuries or distress to the patients.

Complications

The main complication is stress and potential harm to the patient due to an unsafe environment. Alterations not only increase the stress upon the patient, but patients can be at risk of falls, injuries, and perhaps can be a danger to themselves or to others due to their violent behaviors.  A careful evaluation is needed to ascertain the cause while assisting the patient and preventing them from any further distress or injuries.