Anosognosia

Etiology

Typically, as mentioned in the introduction, anosognosia manifests as a neurological sequela following an injury or a lesion to the right parietal lobe; however, the two are not mutually exclusive as the phenomenon of anosognosia can occur with temporoparietal, thalamic, or basal ganglia lesions, as well as in psychiatric disorders. The exact etiology of anosognosia is unknown but is likely due to a derangement of the anatomical or functional monitoring unit that mediates the conscious awareness of deficits. The most likely physiopathologic mechanism is that the brain lesion that causes anosognosia disrupts neurocognitive, secondary integration areas.[3] Structural and functional regions under investigation include the prefrontal cortex (involved in working memory, self-monitoring, and organization), insular cortex (associated with the salience network, emotional processing, and error awareness), and default mode network (includes connectivity between prefrontal, parietal, and cingulate cortices). Damage to these areas can lead to a lack of conscious awareness of cognitive or sensorimotor function loss.

Epidemiology

Anosognosia can occur after acute brain injuries such as strokes or traumatic brain injuries, and can also occur in the absence of any putative brain injury. In stroke patients with hemiparesis, the incidence of anosognosia is 10% to 18%.[4] The term anosognosia can also refer to the lack of awareness seen in psychiatric conditions when patients deny or minimize psychiatric symptoms. It is estimated that 50-90% of patients with schizophrenia and 40% of patients with bipolar disorder demonstrate anosognosia or severe lack of insight.[5] In the setting of neurocognitive disease, 60% of patients with mild cognitive impairment[6] and 81% of patients with Alzheimer's dementia appear to have some form of anosognosia; patients suffering from these conditions deny or minimize their memory impairment.[7]

Pathophysiology

Patients with anosognosia due to brain injury often exhibit a lack of awareness of hemiparesis, hemisensory deficits, 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. The latter consists of the patient's denial that part of their body belongs to them.

Although anosognosia usually accompanies a right parietal, temporoparietal, thalamic, or basal ganglia lesion, recent studies suggest that the deficit sometimes can relate to non-structural changes. These changes cause problems with the connectivity of different parts of the brain.[8]

The fundamental neurophysiologic or psychopathologic problem in anosognosia relates probably to an inability of the patient to update their self-image. Because of a lesion in the brain or dysfunction due to illness, the patient cannot incorporate new information regarding their deficits into their self-image. Therefore, they deny their illness or deficit or downplay its significance.

History and Physical

Typically, health professionals diagnose anosognosia at the bedside by assessing the patient’s knowledge and insight of their symptoms. In subtle cases, it takes time and a long conversation with the patient to uncover anosognosia as patients may rationalize semi-logical reasons for not being able to perform activities on the affected side. In the setting of dementia, patients do not acknowledge or minimize their memory deficits. In the setting of mental illness, patients rationalize aberrant behavior or psychiatric symptoms and often confabulate (i.e. unconsciously prevaricate). This involves the creation of a false answer or response by combining real and imagined details.

Evaluation

When anosognosia is due to structural brain damage, neuroradiological findings typically show damage to the right parietal or 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 shows non-specific findings.

There are publications on an anosognosia rating scale, which rates the level of unawareness of patients with dementia suffering from this condition:

1. Patients easily admit memory loss.
2. Patients admit, sometimes inconsistently, to a small amount of memory loss.
3. Patients are not aware of any impairment in memory.
4. Patients angrily insist that no memory problem exists.

Treatment / Management

There is no specific treatment for anosognosia, but vestibular stimulation seems to improve this condition temporarily. This maneuver probably influences awareness of the neglected side temporarily. Where anosognosia persists, cognitive therapy can help patients better understand and compensate for their deficit.

Differential Diagnosis

Anosognosia differs from denial, a psychological defense mechanism that involves avoiding or rejecting information that provokes stress or pain. With denial, the patient may acknowledge a deficit but minimize its consequences and avoid treatments geared to remedy the deficits. Anosognosia also differs from a more global derangement such as encephalopathy where there may be problems with wakefulness and attention. It differs from other deficits such as visual, sensory, and cognitive deficits which limits the ability of patients to realize their deficit.

Prognosis

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.

Complications

Anosognosia can impair rehabilitation and recovery because patients that lack awareness of a deficit may show less inclination to take part in rehabilitation therapy to tackle the neurological dysfunction. Patients with anosognosia also may suffer more frequent falls due to their lack of awareness of their deficits. Health providers may need to take safety precautions that they see fit in order to avoid injury.