Anton Syndrome MeSH D019575





Disease Entity

Anton Syndrome is a manifestation of bilateral occipital lobe damage in cortically blind patients. These patients lack insight into their disease and deny their blindness. Classically, patients with this syndrome dismiss the diagnosis and confabulate visions. This syndrome differs from Charles Bonnet Syndrome, a disorder in which patients with visual loss experience elaborate, formed hallucinations with preservation of insight into their deficit. [1]

Disease

Named initially for neurologist Gabriel Anton, an Austrian physicist who described patients with complete lack of self-perception of their blindness, including a case of a 69yo dairymaild who had a lesion in both temporal lobes and acquired anosognosia and deafness [1][2]. However, the first cases date to the romans that initially described a case of Harpaste, a slave who denied her blindness. Alternate names are Anton-Babinski, Anton’s blindness, visual anosognosia (impaired awareness of the functional consequences of medical disorders[3]), the latter term coined by Joseph Babinski.[1] Patients may appear to have normal vision due to their detailed confabulation and description of surroundings, often leading to delayed diagnosis of vision loss. The defect becomes apparent when patients are found describing people or surroundings that are not present, or walking into objects, though the patient will continue to deny that they cannot see even when presented with evidence otherwise.

Epidemiology

Anton Syndrome is most commonly secondary to cerebrovascular accident, so is primarily seen in elderly individuals with multiple vascular risk factors.

Though the literature is extremely limited, this syndrome has also been reported in younger age groups when etiology is non-vascular. A case of Anton Syndrome due to MS exacerbation has been recorded in a 24 year old woman.[4] It has also been reported secondary to trauma in a 36 year old woman[5], and obstetric hemorrhage following incomplete abortion in a 19 year old woman.[6]

Etiology

Anton Syndrome is seen secondary to damage to bilateral occipital cortex. It is most commonly reported after cortical blindness due to cerebrovascular accident but has been reported in literature in pregnancy induced hypertensive encephalopathy [7], trauma [5], as result of MS exacerbation [4], among other causes including post cardiac surgery, obstetric hemorrhage, MELAS, cerebral angiography, adrenoleukodystrophy, CNS angiitis and HIV-related progressive multifocal leukoencephalopathy[2].

Risk Factors

Any process causing bilateral occipital lobe blindness can result in Anton Syndrome, though it is a rare presentation.

General Pathology/Pathophysiology

The exact pathophysiology of Anton Syndrome is unknown. Patients with damage to their primary visual cortex bilaterally also have damage to their visual association cortex, which is hypothesized to contribute to their lack of insight to their condition.[8] Another theory is that it is secondary to parietal white matter lesions leading to a disconnection syndrome.[6] Also, as the connection between the damaged visual cortex and operating speech language areas is severed, it is possible that without input, the speech regions of the brain are responsible for confabulating responses.[1]

Primary prevention

There is no specific primary prevention for Anton Syndrome. The most common cause and most irreversible cause of this condition is cerebrovascular accident, therefore prevention should be focused on typical stroke prevention.

Diagnosis

This diagnosis is made clinically based on history of unrealistic confabulation, or clinical proof of vision loss, normal results of fundoscopic exam, and diagnosis of occipital lobe damage.

Physical examination

The physical exam in Anton Syndrome will demonstrate complete loss of vision. Fundoscopy will be unremarkable. Ocular movements will be intact if patients are verbally told which direction to look, however they will not be able to follow a finger or light. Cortically blind patients can potentially maintain perception to hand movements. This is described as the Riddoch Phenomenon, when moving objects are visible but static objects are not [9]. On eye exam, patients with Anton Syndrome however, will not blink in response to threatening hand gestures. [3] Pupillary reflexes will be intact, as occipital lesions are posterior to the lateral geniculate nucleus, and the pupillary pathway will not be affected. Corneal blink reflex is also intact, as this reflex does not depend on cortical input.[6] However, patients will be NLP on acuity testing though they will be completely unaware of their blindness. This lack of awareness can be observed by simply watching or talking to the patient. If the physician asks the patient to describe the physician, the patient may give a completely incorrect visual description. If the physician tells the patient he is extending his hand for a handshake, the patient may extend his hand in the wrong direction.[9] Case reports have mentioned Anton Syndrome seen secondary to a variety of diseases, including hypertensive encephalopathy[7], trauma [5], as result of MS exacerbation.[4] In these circumstances, the exam findings associated with these conditions may also be positive, such as retinal hemorrhages due to hypertensive encephalopathy, optic nerve damage due to trauma, RAPD and/or INO due to MS for example. Patients who suffered from large cerebrovascular events may present with motor or sensory sequelae from cortical damage to shared vascular territories.[1] Anton syndrome should be suspected in patients with a normal structural eye exam and complete lack of visual acuity and lack of awareness of their blindness.

Signs/Symptoms

Patients with Anton Syndrome are often found describing people or surroundings that are not present, or walking into objects, though the patient will continue to deny that they cannot see even when presented with evidence otherwise. One case report described an elderly patient with Anton Syndrome secondary to occipitoparietal stroke who had quick, but incorrect, responses to questioning about the physician’s tie or physical appearance. When left alone with a food tray she would feel for the utensils and feed herself, but required assistance to eat without spillage. Though she accepted this help, she continued to maintain denial of her visual loss.[1] Another case report described an encounter during which the physician told the patient he was extending his hand for a handshake, and the patient reached out in a direction away from the physician.[9]

Diagnostic procedures

Head CT and MRI should be ordered to look for apparent occipital lobe damage, most likely signs of ischemia or hemorrhage. However, if secondary to exacerbation or occurrence of another disease process such as MS, demyelinating lesions may be seen.[4] Complete blindness can be confirmed by demonstration of absence of response to simulation of visual evoked potentials.[9]

Differential diagnosis

The differential diagnosis for Anton Syndrome includes: Charles Bonnet Syndrome, dementia, visual hallucinations due to psychosis (psychiatric or substance induced), malingering/non-organic, confabulation due to Wernicke-Korsakoff syndrome. Patients with Charles Bonnet Syndrome have visual loss due to any cause, and experience elaborate hallucinations with preservation of insight into their deficit, while patients with Anton Syndrome are unaware of their visual loss.[1] Demented patients experience cognitive anosognosia, and are unaware of their memory impairment [10] These patients may confabulate as well, but it is due to their inability to recall the true path of events and not their inability to see. Likewise, patients with Korsakoff Syndrome due to thiamine deficiency also confabulate due to memory deficits. This neuropsychiatric disorder presents with deficits in both anterograde and retrograde memory, with major loss of short term memory and intact sensorium. These patients are not encephalopathic, as opposed to Wernickes patient, and in fact will fabricate stories in clear consciousness [11]. This can be contrasted from Anton Syndrome, as patients have intact immediate memory and will be able to respond accurately to visual acuity examination. Patients with visual hallucinations from psychosis due to substance abuse should cease to have these symptoms after the toxic effect substance wears off. Patients with psychotic disorders are more likely to experience auditory hallucinations which are not associated with Anton Syndrome. Patients who are malingering and in fact have no visual deficit can be identified by an ophthalmologist by using visual evoked potentials which demonstrates intact central visual function. [12]

General treatment

Treatment for Anton Syndrome will depend on the treatment of the assumed causative factor of occipital lobe damage. For example, though it is rarely non-vascular in nature, one patient experienced Anton Syndrome as a result of an MS exacerbation. When treated with IV methylprednisolone and plasmapheresis, she experienced gradual recovery over 2 years which began with a delayed insight to her deficit and eventual restoration of acuity.[4]

Medical therapy

Treatment for Anton Syndrome should focus on correcting the assumed causative factor of damage to the occipital lobe. As this is most commonly secondary to cerebrovascular accident, regular stroke precautions should be taken to prevent future events, including management of vascular risk factors (normalizing blood pressure, blood glucose, lipid levels, smoking cessation etc) and standard pharmacologic interventions such as daily aspirin and statin therapy.

Surgery

There is currently no surgical treatment option for Anton Syndrome.

Prognosis

Case reports have shown good recovery when patients are young, have no history of hypertension or diabetes, have no cognitive, language, or memory impairment.[8] However, based on the limited literature available, in patients with Anton Syndrome as result of bilateral occipital cortical infarction, the prognosis is poor and patients are unlikely to ever fully recover.[1]

References