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Anton's Syndrome

Anton's syndrome is a rare disorder that develops due to deterioration or damage to the occipital lobe. People with this disorder are cortically blind and suffer from confabulation and anosognosia. Therefore, they can no longer process visual input but have a pupillary response to light. Despite people having an apparent visual impairment, they still believe they have their sense of sight. As a result, patients will frequently bump into objects, describe things that aren't there, and confabulate answers about visual stimuli. Anton's syndrome typically occurs after a cerebrovascular event.

 Signs and symptoms 

Acquired cortical blindness is total or partial vision loss, most often due to an absence of blood flow to the visual cortex either from the bilateral or unilateral posterior cerebral artery or damage to the occipital lobes. Common explanations for cortical blindness in minors are traumatic brain injury to the occipital lobes, perinatal ischemia, or congenital abnormalities of the occipital lobes. However, typically in adults, cortical blindness can be due to several different disorders: stroke, severe hypoglycaemia, eclampsia, hyponatremia, or occipital lobe epilepsy, for example.

Confabulation is the creation of false memories without ill intent to deceit or lie. This symptom occurs due to poor cognitive function or brain damage; investigators are unsure which portion of the brain causes this but believe the frontal lobe or the basal forebrain may be involved. Researchers theorise that people with Dementia tend to confabulate memories to replace the ones they lost. Therefore, patients with Anton's Syndrome are overcompensating for their lack of visual input. Gabriel Anton believed that functioning speech and language areas are disconnected due to damage to the occipital lobes and visual pathways; in response, the functional speech areas may confabulate when there is no functional visual input.

Anosognosia is the denial or lack of insight, which can be a symptom of many severe mental illnesses. For example, people will still dismiss and disregard any evidence that they suffer from a disorder. Anosognosia is associated with damage to the frontal lobes, which are critical for self-awareness and perception. Damage to the frontal lobes may cause anosognosia because individuals cannot update their perception of themselves. Another theory to explain why this happens is damage to the conscious awareness system positioned in the bilateral parietal lobes, which oversees sensory input. Furthermore, one other system involves the frontal lobes, which are connected to the conscious awareness system. These two systems work together in carrying out complex cognitive activities. In Anton's syndrome, when the association pathways between the visual cortical region and the conscious awareness system are damaged, this could be a reason for the loss of awareness.

 Assessment 

Diagnosing Anton's Syndrome may be difficult, considering some of the symptoms may be misconstrued as delusions or hallucinations, especially since it is uncommon. In addition, Anton's could be misdiagnosed for many conditions such as Charles Bonnet Syndrome, Schizophrenia, Alzheimer's disease, or Dementia. Hence, diagnosing is essential to provide the most appropriate care.

 Assessment tests: 

Imaging:

fMRI can be used to map the visual cortex, and CT imaging allows more detailed information about brain tissue and structure. In addition, these scans can localise damage to the occipital lobes to confirm the cause of vision loss.

Cognitive testing:

Neurological exams can localise neurologic diseases and evaluate potential diagnoses. For example, a neurological evaluation can assess visual field defects, cranial neuropathies, double vision, pupillary response and abnormalities, ptosis, and vision loss. Consequently, the exam can rule out any other diagnoses and ailments. A Neuro-ophthalmology exam would be beneficial to perform alongside a neurological evaluation. The physician would assess lid retention, bulging of the eyes (proptosis), and pupillary response and inspect the orbits to check for glaucoma.

Visual evoked potentials - the examination records electrical potentials from the scalp residing over the visual cortex, extracted from an EEG examination through signal averaging. Visual evoked potentials are performed to assess the optic nerves' functionality and pathways to the visual and occipital cortex. In addition, it can detect any abnormality affecting the brain's visual cortex or visual pathways, such as cortical blindness.

NVCL-20 - Nijmegen-Venray Confabulation List-20 is a 20-item scale that examines spontaneous confabulation, provoked confabulation, memory, and orientation. The scale is the first of its kind to assess spontaneous confabulation.

The Scale to Assess Unawareness of Mental Disorder (SUMD) is based on a dimensional and quantitative design using a semi-structured interview to evaluate if patients have insight into their conditions. SUMD assesses global insight, the symptoms, and the cause of symptoms (attribution). The scale divides into two categories; the awareness and attribution of mental conditions. Awareness in this scale is defined as the ability to identify that a disorder is present, and attribution refers to an explanation of the reason or cause of the symptoms they have. This method allows researchers to distinguish between patients' ability to recognise their symptoms from their capacity to explain the cause.

 History 


 * In 63 CE, Roman philosopher Seneca described Harpaste, a woman who became blind but denied her condition, which meets the criteria for Anton's.
 * Michel de Montaigne, a French renaissance writer, mentioned a man who continuously denied his blindness in his second book, which he wrote between 1580-1588.
 * Von Monakow (1885) and Dejerine and Vialet (1893) first depicted anosognosia in patients with cortical blindness.
 * Between 1887 and 1889 Sergei Korsakoff, when describing patients with Korsakoff syndrome, created the term confabulation.
 * In 1895, Gabriel Anton first described a woman with anosognosia with cortical deafness and other individuals with cortical blindness or deafness who dismissed their circumstances.
 * In 1914, Joseph Babinski coined the term anosognosia for people who denied their deficits.
 * Adolf Meyer (1920) noted that the causal factor of Anton's Syndrome was an occipital lobe infarction and postulated compression of branches of the posterior cerebral artery.

 Research 

Researchers described a patient with Anton's syndrome who had suffered a traumatic head injury which damaged the optic nerve. The denial of monocular blindness, generalised anosognosia, and confabulation was apparent within the patient. This case demonstrates that the condition may be associated with cortical blindness from a peripheral lesion even when it is not associated with either delirium or Dementia. The investigators suggested that bifrontal dysfunction may be the most vital factor causing Anton's syndrome.

Furthermore, a neurological evaluation of a 79-year-old man showed cloudy consciousness and poor speech, and he also exhibited facial paralysis and quadriplegia. Initially, treatment was for symptomatic therapy and dehydration. The next day, the man became more alert and clear-headed but was found blind and denied any impairment. However, further testing involving a brain CT exam detected infarcts in the bilateral temporal-parietal-occipital junction and a haemorrhagic transformation, a common complication after an acute ischemic stroke. Physicians believe that his condition was consistent with Trousseau and Anton's syndrome. After the formal diagnosis, the patient continued treatment with oral rehydration solution, blood sugar control and symptomatic treatment. At the time of the patient's discharge, he partially recovered his right visual field and was fully aware of his condition.

 Treatment 

Currently, there is no cure for Anton's Syndrome, but there are strategies that may positively impact patients. Research suggests that a traditional compensatory approach may be the most appropriate, which includes retraining sensory pathways and screening for patients' awareness through checking orientation. Additionally, mobility and environmental adaptations can primarily aid in patients improving their functionality. Also, researchers' findings support that self-awareness increases participation in treatment and rehabilitation.

Moreover, a study on the rehabilitation of Antons suggests that regular counselling sessions by psychological counsellors may have enhanced patients' insights into their condition. Compensatory strategies are typically taught to improve the day-to-day lives of people with Anton's, but they do not improve their eyesight. Visual restorative therapy may be viable as it enhances vision by stimulating viable neurons near the occipital cortex. However, visual recovery for Anton's syndrome can differ but typically is minimal. Treatment for visual recovery relies heavily on aetiology, and since a cerebrovascular event most commonly causes Anton's, this reduces the chances of patients regaining their vision. Nevertheless, a better prognosis has been reported in cases of treated hypertensive encephalopathy and cortical hypoperfusion when they cause the manifestation of Anton's syndrome.

Previous research suggests that individuals with Anton's pose a risk to themselves as they are less cooperative with treatment and can limit functional improvement. As a result, treatment options are limited, but research into the neuroplasticity of the somatosensory system has shown promise but has not yet been used for Anton's syndrome.

Reducing the impact of symptoms includes working with mental health professionals to provide effective interventions for people with confabulation. Whilst, confabulation may dissipate without rehabilitation, most patients will need treatment.

A research study analysed the effectiveness of caloric vestibular stimulation (CVS) on Schizophrenia patients with anosognosia. Results showed that a single session of left cold CVS improved impaired insight; however, right cold CVS may have exacerbated symptoms. Therefore, left-cold caloric vestibular stimulation may be an effective measure when treating anosognosia.

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