Introduction

Imagine waking up one morning unable to recognise your fingers. This is just one of the perplexing symptoms of Gerstmann Syndrome, a rare neurological disorder. With problems rooted in the parietal lobe, Gerstmann Syndrome was so called by Josef Gerstmann, who observed his patients have cognitive deficits in writing and counting.¹ Gerstmann Syndrome is thought to be caused by damage to the left parietal lobe of the angular gyrus.² To understand the complexity of the syndrome, the relationship between dysfunction of the parietal lobe and the symptoms of Gerstmann Syndrome must be considered. 

Understanding gerstmann syndrome

Gerstmann Syndrome can be the result of either brain damage or a developmental disorder.³ Common causes of the disease can include stroke, tumours, multiple sclerosis, and an aneurysm of an artery. Research has suggested that other causes could include alcoholism, anaphylactic shock, lead intoxication, and carbon monoxide poisoning.⁴

There are four main symptoms of the syndrome:^{1, 2, 4}

1. Agraphia — loss of the ability to write, or difficulty in doing so
2. Acalculia — difficulty in performing simple calculations and arithmetics
3. Finger agnosia — inability to identify one’s fingers
4. Left-right disorientation — difficulty in distinguishing between left and write 

Role of the parietal lobe in gerstmann syndrome

The parietal lobe

As seen in Figure 1, the parietal lobe is located behind the frontal lobe and above the temporal and occipital lobes.⁵ Located at the top of the brain, it is present in both hemispheres.⁶

The parietal lobe is responsible for processing sensory information and spatial awareness. Proprioception, the body's ability to sense itself and its movements, is controlled by the parietal lobe. Without needing to see parts of the body, areas in the parietal lobe enable your body to sense where they are based on touch.⁷

Figure 1. An image depicting the brain with areas shaded showing the 4 lobes, including the parietal lobe.⁶

The parietal lobe can be divided into two regions—the anterior parietal lobe and the posterior parietal lobe. The primary sensory cortex is located in the anterior parietal lobe. It is here where sensory information is sent once it has been detected by parts of the body.⁵ The sensory cortex processes signals of pain, temperature, pressure, simple touch, etc. This information is then relayed to the appropriate action centres in the brain. The posterior parietal lobe contains the secondary somatosensory cortex, which integrates somatosensory information with other information such as auditory and vision. Through integration, the posterior parietal lobe facilitates the preparation and execution of several functions, including learning, language, spatial recognition, sensorimotor planning and stereognosis.⁵ 

Dysfunction and symptoms

Dysfunction in the parietal lobe, particularly the left angular gyrus, can lead to the symptoms of Gerstmann syndrome:

Link to agraphia

The angular gyrus is responsible for integrating both the visual and motor information necessary to act in writing. Damage in this area prevents the integration of the different sensory inputs, inhibiting the motor planning required to write.⁸ 

Link to acalculia 

The angular gyrus plays a key role in recalling numbers and visual information needed for calculations..⁸ Damage to this area impairs the ability to understand numbers and perform calculations, thus leading to acalculia.⁹

Link to finger agnosia 

The left angular gyrus is responsible for visuospatial navigation and the body's perception of itself, including the ability to identify parts of the body as our own. Damage to this area can lead to finger agnosia, the inability to recognise one's fingers.⁸

Link to left-right disorientation

As the left angular gyrus controls visuospatial processing and awareness, damage to the parietal lobe prevents the brain from distinguishing between left and right, thus causing left-right disorientation.⁸

The presence of the 4 symptoms without mental underdevelopment will earn a diagnosis of Gerstmann Syndrome.³ Some individuals may not have all 4 symptoms. In this instance, extra care must be taken to eliminate any other cognitive defects that could be causing the deficiency. Furthermore, the severity of the symptoms differs between individuals. 

Diagnostic and clinical aspects

Diagnostic criteria

A clinical evaluation will be carried out to diagnose Gerstmann syndrome. This will involve a thorough medical history, looking particularly for any signs of a neurological condition, stroke, brain damage,  or any other incidents that could affect the structure and function of the parietal lobe. Additionally, a physical examination will be carried out, observing for any of the 4 symptoms of Gerstmann Syndrome. This could involve watching an individual as they write (test for agraphia), having them undertake mathematical calculations (test for acalculia), and asking them to put up a specific finger and name it (test for finger agnosia), or finally asking them to distinguish their left from their right (test for left-right disorientation). Other aspects of cognitive function such as speech and memory are carried out to rule out other cognitive dysfunctions. A differential diagnosis like this is essential for efficient treatment.¹⁰ 

Neuroimaging techniques

Magnetic resonance imaging (MRI) can be used to identify any structural lesions present in the parietal lobe, in particular the angular gyrus.¹⁰ An alternative neuroimaging technique that can be used alongside or in place of an MRI is a Computed Tomography (CT) Scan. Whilst less detailed than an MRI scan, a CT scan can be used to detect lesions, tumours and brain bleeds.¹⁰ Other imaging techniques that can be used include Positron Emission Tomography (PET) and Electroencephalography (EEG).¹⁰

Management and treatment

There is no cure for Gerstmann syndrome, therefore, treatment is targeted at the symptoms in hopes of minimizing or eliminating them.

• Treatment for agraphia—Research has found that high doses of speech and language therapy are effective in improving writing ability¹¹
• Treatment for acalculia—The individual should relearn the concept of numbers, then they should move on to learning how the numbers relate to one another, and finally they should try to solve arithmetic problems¹²
• Treatment or finger agnosia—specialised therapies and counselling can help to manage finger agnosia, such as practising with visual cues to identify a finger. Special gloves may even be worn with numbered fingers to identify each finger
• Treatment for left-right disorientation—repeated teaching of left and right could help with the disorientation. Individuals may choose to write left or right on their body to distinguish between the two

In a few cases, the cause of the syndrome could be removed. For example, if it is caused by a tumour, the tumour may be removed, thus reducing or eliminating the symptoms.⁴

Treatment can better the prognosis for people with Gerstmann Syndrome as it improves their cognitive abilities, bettering their performance in school and the workplace. 

Summary

In summary, damage to the parietal lobe, particularly the left angular gyrus, causes Gerstmann Syndrome, a disorder characterised by 4 symptoms: agraphia, acalculia, finger agnosia, and left-right disorientation. Understanding the link between damage to the left parietal lobe and the symptoms of the syndrome demonstrates how these seemingly unrelated symptoms appear together, whilst also highlighting the profound role the parietal lobe plays in an array of cognitive processes. Furthermore, by recognising the impact of parietal lobe damage on cognitive symptoms, the importance of understanding brain function becomes evident. Additional research must be carried out as there is currently no cure for Gerstmann Syndrome. Developing a cure will no doubt improve the quality of life of those who suffer from Gerstmann Syndrome.