Anosognosia is a neurological condition where the patient is unaware of his/her neurological deficit or psychiatric condition. The French neurologist, Joseph Babinski, first described anosognosia in 1914, and it is associated with mental illness, dementia, and structural brain lesion such as stroke. It can affect the patient’s conscious awareness of deficits involving judgment, emotions, memory, executive function, language skills, and motor ability.
Typically, anosognosia is associated with a lesion in the right parietal lobe but can occur with temporoparietal, thalamic, or basal ganglia lesions. The exact cause of anosognosia is unknown but is likely due to a derangement the anatomical/functional monitoring unit that mediates the conscious awareness of deficits. The brain lesion that causes anosognosia is thought to disrupt neurocognitive secondary integration areas. Damage to these areas can lead to a lack of conscious awareness that cognitive or sensory-motor function has been lost.
Anosognosia can occur after acute brain injuries such as stroke or traumatic brain injury but also can occur in other conditions that damage the brain. In stroke patients with hemiparesis, the incidence of anosognosia is 10% to 18%. The term anosognosia also describes the lack of awareness seen in psychiatric conditions when patients deny or minimize psychiatric symptoms. It is estimated that 50% of patients with schizophrenia and 40% of patients with bipolar disorder have anosognosia. In the setting of dementia, 60% of patients with mild cognitive impairment and 81% of patients with Alzheimer disease appear to have some form of anosognosia where patients suffering from these conditions deny or minimize their memory impairment.
Patients with anosognosia due to brain injury often exhibit a lack of awareness of hemiparesis, hemisensory deficit, neglect, memory deficits, and language deficits. Patients may be unaware of one deficit while recognizing others. Anosognosia can co-occur with somatosensory neglect (asomatognosia), which also localizes to the right parietal lobe, and is typically characterized by denial by the patient that part of his/her body belongs to him/her.
The exact mechanism leading to anosognosia is not clear. Recent studies suggest that the deficit may be related to non-structural changes. These changes are characterized by problems with the connectivity of different parts of the brain.
The fundamental problem in anosognosia may be related to an inability of the patient to update his/her self-image. Because of a lesion in the brain or dysfunction due to illness, the patient is unable to incorporate new information regarding their deficits into his or her self-image. Therefore they deny their illness or deficit or downplay its significance.
Typically, the diagnosis of anosognosia is made at the bedside by assessing the patient’s knowledge of his/her deficits. In subtle cases, anosognosia may be noted when patients make excuses for not performing activities on the affected side or does not acknowledge the paralysis. In the setting of dementia, patients do not acknowledge, or they minimize memory deficits. In the setting of mental illness, patients rationalize aberrant behavior or psychiatric symptoms. Patients with this condition often confabulate. This involves the creation of a false answer or response by combining real and imagined details.
When anosognosia is due to structural brain damage, neuroradiological findings typically show damage to the right parietal, right temporoparietal region. Less common are lesions in the thalamus, basal ganglia, or left parietal region. Neuroimaging in dementia typically shows more global brain atrophy. Neuroimaging in psychiatric disorders usually show non-specific findings.
An anosognosia rating scale has been developed to rate the level of unawareness of patients with dementia suffering from this condition:
There is no specific treatment for anosognosia, but vestibular stimulation has been shown to improve this condition temporarily. This maneuver is thought to influence awareness of the neglected side temporarily. In cases where anosognosia persists, cognitive therapy can be used to help patients better understand and compensate for his or her deficit.
Anosognosia must be distinguished from denial, a psychological defense mechanism that involves avoiding or rejecting information that provokes stress and/or pain. With denial, the patient may acknowledge a deficit but minimize its consequences as well as avoid treatments geared to remediate the deficits. Anosognosia must also be distinguished from more global derangement such as encephalopathy where there may be problems with wakefulness and attention. It must also be distinguished from other deficits such as visual, sensory and cognitive deficits which may limit the capacity of patients to become aware of his/her deficit.
When anosognosia is due to a focal structural lesion of the brain, it typically resolves over time, though it can persist over the long-term. When anosognosia is due to mental illness or dementing illness, it may persist and lead to poor compliance with medication regimens.
Anosognosia can impair rehabilitation and recovery because patients that lack awareness of a deficit may show less inclination to participate in rehabilitation therapy to remediate the neurological condition. Patients with this condition may also be inclined toward falls because of a lack of awareness of their deficits. Safety precautions need to be taken to avoid injury.
Recently an ethical framework was described by A.R. Egbert to involve patients with anosognosia in their rehabilitation treatment. Rehabilitation specialists must be aware of the presence of this condition because it may affect the outcome of their treatment plan.
Patient and family members should be educated about the presence of anosognosia. This condition poses special difficulties for family members when the patient fails to acknowledge or minimize his or her condition. Issues such as driving, handling money, walking without assistance may become areas of conflict. It is important that a thorough safety evaluation is done to avoid injury to the patient suffering from anosognosia. In general, simplifying tasks, maintaining a positive approach, showing concern and empathy, and providing a structured environment are all helpful to avoid negative outcomes.
It is very important for emergency clinicians to be aware of this condition. For example, in the setting of acute stroke, the timing of symptom onset is crucial to the administering of thrombolytic therapy. If the patient is unaware of their deficit, he/she may not give accurate information of the exact time of stroke symptom onset. In that situation, collateral history from a family member is crucial to making an informed treatment decision.