Introduction 

In 1924, an Austrian neurologist Josef Gerstmann reported a case of a 52-year-old woman who was unable to distinguish between her fingers and differentiate between her left and right fingers when asked to move them, write, or calculate.¹ Gerstmann syndrome is a rare neurological disorder defined by a tetrad of the following symptoms:²

• Finger agnosia
• Acalculia
• Left-right disorientation
• Agraphia

This article will illustrate the impacts of the Gerstmann syndrome, with a focus on the neurological basis underlying this disorder. 

Features of gerstmann syndrome

Symptoms

The main symptoms of Gerstmann syndrome include cognitive difficulties due to impairments in different brain regions. “Pure” Gerstmann syndrome is seen in affected individuals who display all of the following four symptoms without other cognitive impairments (NORD). 

Finger agnosia 

Finger agnosia refers to the inability to recognise, name, or distinguish between your fingers or another person’s fingers.³ 

Left-right disorientation

When you are unable to differentiate between the left and right sides of your own body or another person’s body, this is known as left-right disorientation.³ 

Agraphia

Agraphia (also called dysgraphia) refers to the impaired ability to write using your hands.³ 

Acalculia 

Acalculia refers to the inability to calculate using mathematical rules, such as performing simple arithmetic calculations. It may be due to verbal or written difficulties, and has been linked to semantic aphasia (difficulty understanding words with spatial descriptions like “above” or “below”).³

Related cognitive impairments and symptoms

Some adults may also experience aphasia, where they face difficulties in speaking, reading, writing, and understanding speech. Children are diagnosed with developmental Gerstmann syndrome, which is a type of learning disorder. They may have poor handwriting and spelling, and face difficulties in doing maths (addition, subtraction, multiplication, and division). Some children may even experience constructional apraxia, where they are unable to copy or trace simple drawings. They may also experience alexia, where they have difficulty understanding written words and impaired reading abilities. 

Frequency of affected populations

Gerstmann syndrome affects people assigned male and female at birth in equal numbers and may develop at any stage of life; however, due to the rare nature of the disorder, the frequency of the affected populations is unknown. Those affected by Gerstmann syndrome rarely present all four symptoms, and most of them commonly experience two to three symptoms of this disorder (“incomplete” Gerstmann syndrome).³ There has been no evidence so far suggesting that this disorder is inheritable (runs in families) (NORD). Moreover, some children with a high level of intellectual functioning might also be susceptible to this disorder.

Brain regions involved in gerstmann syndrome  

The parietal lobe is a key brain region involved in the processing and use of sensory information in order to understand the world around us. Functions of the parietal lobe include the perception of self through touch, spatial awareness of self and objects in your environment (like differentiating between left and right), compiling sensory information (touch, taste, smell, sight, and hearing), and the execution of complex learned movements, like performing mathematical calculations by hand. 

The left angular gyrus is a structure in the posterior parietal lobe which is involved in the semantic processing and retrieval of arithmetic knowledge during problem-solving activities.³ The position of the left angular gyrus exists in a junction that connects the parietal, temporal, and occipital lobes.⁴ But why is the left side relevant? This is because the dominant hemisphere controls the contralateral side of the body. In other words, the left hemisphere is dominant in right-handed individuals and vice versa. The left hemisphere of our brain is commonly associated with communication like speech and language, problem-solving, memory, and analytical skills. The left posterior parietal lobe is associated with lexical functions like words and numbers, while the right posterior parietal lobe is associated with spatial functions like identifying the location of dots.³ 

Causes of gerstmann syndrome

Gerstmann syndrome is commonly caused by damage to the posterior part of the parietal lobe in the dominant hemisphere of the brain (usually the left, but may occur in the right hemisphere as well). The angular gyrus was initially identified as the prime location of damage, and due to its position, functions of the temporal and occipital lobes were also affected, resulting in symptoms like finger agnosia, right-left disorientation, agraphia, and acalculia.³ Therefore, Gerstmann syndrome was also called the angular gyrus syndrome in early research.³ However, studies have found that other brain structures are involved, such as the supramarginal gyrus or the intraparietal sulcus (for finger agnosia and acalculia) and superior parietal gyrus (for agraphia).² There has been much debate and research on the structures involved in Gerstmann syndrome due to the majority of cases demonstrating an “incomplete” tetrad of symptoms.³ Research has also revealed other associated causes of Gerstmann syndrome, such as ischemic stroke, tumours, multiple sclerosis, aneurysm, cortical atrophy, and progressive multifocal leukoencephalopathy; toxic levels of alcohol, carbon monoxide, and lead in the body have also been implicated.² 

The “pure” form of Gerstmann syndrome is suggested to be caused by a disconnection of the fibre tracts in separate networks located in the white matter of the parietal cortex.³ Considering the prominence of “incomplete” Gerstmann syndrome cases, recent literature has suggested that damage to the angular gyrus generally disrupts normal sensory processing and results in acalculia, finger agnosia, left-right disorientation, and semantic aphasia (not agraphia).³ Agraphia is suggested to appear only when the damage extends to the superior parietal gyrus structure in the brain.³ 

Summary

Gerstmann syndrome is a neurological disorder consisting of four main symptoms, namely finger agnosia, left-right disorientation, agraphia, and acalculia. This disorder affects people assigned male or female at birth equally and may appear at any stage in life. Children who exhibit similar symptoms are diagnosed with developmental Gerstmann syndrome which manifests as a type of learning disorder. Damage to the parietal lobes of the brain results in the symptoms of Gerstmann syndrome. The left angular gyrus was identified as a prime site of the disorder but other structures have also been implicated towards the appearance of symptoms. Due to the prominence of an “incomplete” form of Gerstmann syndrome, studies have found that agraphia may only appear when damage extends to the superior parietal gyrus structure in the brain. Since there is no cure for Gerstmann syndrome, it is important to speak to a medical professional about possible treatments and therapies to support those affected by the disorder.