Simultanagnosia is the inability to perceive more than one object at a time. Patients are capable of identifying individual elements of a complex scene but have great difficulty in understanding what is occurring overall within the scene (i.e., “cannot see the forest for the trees”). The symptoms of simultanagnosia can be mild, moderate or in some cases severe enough to compromise one’s ability to function well in everyday life. Simultanagnosia most often results from bilateral damage to the parieto-occipital regions of the brain, and patients will often have homonymous or juxtaposed homonymous visual field deficits due to involvement of the occipital lobe(s).
Simultanagnosia may result from any etiology that causes damage to these areas (e.g, ischemic, inflammatory, hemorrhagic, infectious, traumatic, neoplastic, neurodegenerative). Simultanagnosia may present as an isolated syndrome or in conjunction with other neurological deficits. For example, in the Bálint syndrome in addition to the simultanagnosia there may be optic ataxia, and oculomotor apraxia. Standardized simultanagnosia testing figures (e.g., “The Boston Cookie Theft” or “The Telegraph Boy.”) may be useful in the clinic to identify affected patients.
Interestingly, one test that ophthalmologists are already using for color vision, the Ishihara color plates can be used to detect simultanagnosia. Despite normal color and hue discrimination ability, patients with simultanagnosia may fail to correctly identify any Ishihara color plates, including the test plate. Notably, this is not due to a lack of color vision but rather an inability to perceive the individual colored dots in the Ishihara figures as a collective whole resulting in an inability to recognize the numbers or figures on the color plates.
History of the disease
Simultanagnosia was first described in a case report by Rezsö Bálint, a Hungarian physician, in 1909. Bálint studied the patient for more than 2 years, and noted that the patient suffered from psychic paralysis of gaze, optic ataxia, and spatial disorder of attention, the latter later being termed ‘simultanagnosia’ by Wolpert in 1924. Bálint noted that the patient was constrained to seeing only a single object at a given time and that this was irrespective of the size of the object. Upon postmortem examination, Bálint noticed extensive bilateral damage to the parietal lobes and upper parts of the occipital and temporal cortices.
Depends on the underlying etiology.
Simultanagnosia most commonly results from bilateral lesions in the parieto-occipital regions. In rare cases, unilateral right-sided parieto-occipital lesions, bilateral occipital lesions, and unilateral parietal lesions may also produce the symptom. In the acute setting the most common cause is cerebral hypoperfusion as the parieto-occipital region is a watershed area between the middle and posterior cerebral arteries. Other etiologies include invasive tumors, traumatic brain injury, and neurodegenerative conditions such as Alzheimer disease. Bálint syndrome, a disorder defined by the presence of simultanagnosia, optic ataxia, and oculomotor apraxia, is also associated with bilateral parieto-occipital lobe injury; however, the neuroanatomic distinctions between full Bálint syndrome and isolated simultanagnosia are not yet well understood. Generally, Bálint syndrome is associated with more extensive damage with respect to isolated simultanagnosia. Simultanagnosia may be the initial presenting symptom of neurogenerative disease (e.g. Alzheimer disease) and may present to ophthalmology as vague difficulties with their vision. Although the structural eye exam is typically unremarkable, formal perimetry may disclose a homonymous or juxtaposed homonymous visual field defect. The Ishihara color plates as noted above also may be a useful screening test in this setting.
Risk factors for simultanagnosia depend on the etiology (e.g. vasculopathic disorders like hypertension, diabetes mellitus, hyperlipidemia), neurodegenerative risk factors, or trauma.
The precise mechanism resulting in simultanagnosia remains poorly understood. However, there are several proposals such as a visual attentional deficit, which is reasoned anatomically by the fact that the parietal lobe is responsible for the visuospatial attention system. Others have argued that simultanagnosia is due to an inability in matching an object’s identity with the location occupied within the visual field.
There are currently no formal diagnostic criteria for simultanagnosia. Nevertheless, symptoms of simultanagnosia are evaluated using complex visual pictures; “The Boston Cookie Theft” or “The Telegraph Boy” are commonly used. These pictures include many elements and when thoroughly examined display an understandable scenario. Patients with simultanagnosia will fail to understand the overall scenario and will instead simply identify various components of the picture. If symptoms of simultanagnosia are elicited, further neurologic workup may be warranted in the form of brain imaging to evaluate for parieto-occipital damage.
As noted above simultanagnosia is most commonly a result of bilateral parieto-occipital damage but there are many different etiologies that may result in the symptom in this location.
The history depends on the underlying etiology. Acute onset of symptoms suggests ischemia including global hypoperfusion versus a painless and progressive course which suggests neurodegenerative disease. Patients with underlying brain neoplasm in the parieto-occipital region may have other focal localizing or non-localizing (from increased intracranial pressure) symptoms and signs.
Simultanagnosia may present in isolated forms or in conjunction with other neurological symptoms as is seen in Bálint syndrome. Therefore, it is important to evaluate for other neurological deficits, such as optic ataxia and oculomotor apraxia. An ophthalmologist should probably refer patients with this symptom to a neurologist for further evaluation and management.
Patients may be incapable of correctly identifying any Ishihara color plates, including the test plate. This is not due to a lack of color vision however. It is due to the patient’s inability to combine the dots into a whole figure in order to correctly read the plates. When further prompted after having failed to correctly identify the figure on an Ishihara color plate, patients will often be able to correctly identify the colors represented on the plates.
Symptoms of simultanagnosia are characterized by difficulty in perceiving multiple elements of a complex visual scene. Patients may simultaneously have visual field deficits due to occipital lobe damage. Patients may complain of frequently bumping into objects, problems with depth perception, or reading. These symptoms may occur despite normal (20/20) visual acuity and an otherwise normal structural eye exam.
Neuroimaging (preferably magnetic resonance imaging (MRI) of the head) typically shows evidence of bilateral occipitoparietal damage (e.g., neoplasm, stroke, hemorrhage, cortical atrophy). Diffuse weighted imaging MRI and apparent diffusion coefficient MRI are especially useful modalities when evaluating for evidence of acute parenchymal ischemia. Computed tomography (CT) scan may be the best initial neuroimaging test however in patients with acute ischemia or trauma to exclude intracranial hemorrhage.
Treatment varies depending upon the overlying etiology and includes preventing further damage to the parieto-occipital regions. Furthermore, low vision rehabilitation may improve symptoms of simultanagnosia.
There is not currently any medical therapy for the treatment of simultanagnosia.
Surgery is only indicated if the overlying etiology justifies its usage, such as in the case of hemorrhage or tumor.
Prognosis of patients with simultanagnosia is variable and depends upon the extent of brain damage. There is evidence that some level of recovery is possible with rehabilitation, but many patients will continue to experience difficulties.
1. Journal of Neuro-ophthalmology : https://journals.lww.com/jneuro-ophthalmology/pages/default.aspx
2. American Academy of Neurology : https://www.neurology.org/
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