Gerstmann syndrome (GS) is a neuropsychological syndrome characterized by four cardinal signs: (1) agraphia, (2) acalculia, (3) finger agnosia, and (4) left-right disorientation.
It was first reported in 1924 by Josef Gerstmann in a 52-year-old woman. Also called angular gyrus syndrome, it is widely recognized in neurological literature. However, its validity as an independent clinical entity is debated. Benton criticized that the strength of association among the four signs is comparable to that of other combinations of cognitive deficits 1).
Epidemiological data are scarce, but the pure form (all four signs without other deficits) is rare. Incomplete forms and cases accompanied by aphasia, alexia, apraxia, or sensory disturbances are more common 2).
There is also a developmental Gerstmann syndrome (DGS) recognized in children as a type of learning disability, which tends to include constructional apraxia.
It is more common in adults, but can also be seen in children as developmental Gerstmann syndrome (DGS). DGS is a type of learning disability that tends to involve difficulties with writing and calculation, as well as constructional apraxia. Unlike adult GS, the prognosis in DGS may not be as favorable.
The four cardinal signs of GS are evaluated as independent neuropsychological disorders.
Finger Agnosia
Definition: Inability to name, move, or touch a specified finger.
Features: Bilateral, prominent in the central three fingers (index, middle, ring). May involve toes (digit agnosia). Visual impairment is an exacerbating factor. Can occur with the examiner’s fingers or images of fingers.
Assessment: Tends to become more pronounced under non-visual conditions (eyes closed) during tactile identification4).
Left-right disorientation
Definition: Inability to distinguish left from right on oneself and the examiner.
Features: Discrimination of front/back and up/down remains intact. Impaired both on one’s own body and on others’ bodies4).
Assessment: Two-step commands (e.g., “Point to my left shoulder with your right hand”) are useful for diagnosis. Exclusion of visuospatial disorders is important.
Agraphia
Definition: Inability to write intended content. Considered a disorder of motor planning (a type of apraxia).
Features: Copying and spelling abilities may be relatively preserved. Difficulty is prominent in dictation of sentences and drawing pictures1).
Assessment: Test both spontaneous writing and writing from dictation.
Acalculia
Definition: Inability to perform oral and written calculations.
Features: Considered the most variable symptom among the four cardinal signs. Subtraction, multiplication, and division are particularly impaired 1). An association with semantic aphasia has been noted.
Assessment: Evaluate using both written calculation (e.g., 85-27) and mental arithmetic (oral multiplication).
It is an inability to correctly name a specified finger or identify which finger has been touched. It is most prominent in the three middle fingers (index, middle, ring) and is often bilateral. It may also involve the toes. Tactile identification under eyes-closed (non-visual) conditions becomes more difficult 4).
GS is caused by a lesion in the parietal lobe of the dominant hemisphere (usually left) or by disconnection of white matter tracts. The underlying diseases are diverse.
The classification of each etiology is shown below.
| Classification | Main causes |
|---|---|
| Local lesions | Ischemic stroke, cerebral hemorrhage, tumor, aneurysm, PML, multiple sclerosis |
| Diffuse/toxic | Alcohol, carbon monoxide, lead |
| Autoimmune | Anti-NMDA receptor encephalitis |
| Other | Parietal lobe epilepsy (transient GS), iatrogenic (after cerebral angiography) |
Ischemic stroke is the most common cause. The middle cerebral artery supplies the parietal and frontal lobes, and infarction in this area can cause GS. GS has also been reported with infarction of the inferior frontal gyrus 1).
Tumors: In a case of a 7.6 cm meningeal hemangiopericytoma compressing the left parietal lobe, pure GS appeared, and all four signs disappeared within one week after complete resection 2).
Autoimmune encephalitis: Cases have been reported where Gerstmann syndrome (GS) appeared as the initial symptom of anti-NMDA receptor encephalitis. MRI showed no clear lesions, but IMP-SPECT confirmed hypoperfusion in the left hemisphere 5).
Regarding lesion location, classically, damage to the dominant hemisphere’s inferior parietal lobule including the angular gyrus (Brodmann area 39) has been considered the cause. However, recent studies have shown that GS can occur even with only 1.7% damage to the angular gyrus, and disconnection of white matter tracts is now considered the main mechanism 4) (see Pathophysiology section).
Parietal lobe lesions may involve difficulty maintaining fixation and simultaneous agnosia.
It can be reversible depending on the etiology. Cases have been reported where all four symptoms completely disappeared within one week after surgical resection of a tumor 2), and complete recovery to MMSE 30/30 after immunotherapy (steroids, plasma exchange, cyclophosphamide) for autoimmune encephalitis 5). On the other hand, after stroke, improvement is often only partial.
The diagnosis of GS is based on the confirmation of the four cardinal signs through neuropsychological tests.
The indications and characteristics of each imaging modality are described below.
| Imaging Modality | Characteristics/Indications |
|---|---|
| MRI (first choice) | Identification of structural lesions. Acute infarction appears as restricted diffusion. |
| CT | Emergency option. Infarct appears as low-density area |
| Diffusion tensor imaging (DTI) | Evaluates white matter tract disruption. Visualizes disruption of SLF, corpus callosum, and U-fibers1) |
| Single-photon emission computed tomography (SPECT) | Detects decreased cerebral blood flow. Useful even when MRI shows unclear lesions5) |
DWI (diffusion-weighted imaging) can depict ischemic changes as high signal within hours of onset. Magnetic resonance angiography (MRA) and cerebral angiography identify the responsible vessel (e.g., middle cerebral artery).
Electroencephalography (EEG): Used to detect slow waves in the parietal region and evaluate epileptic GS.
There is no curative treatment for GS. Management focuses on symptom control, rehabilitation, and treatment of the underlying cause.
In post-stroke GS cases, symptoms may persist for 4 months, but daily living independence can significantly improve through compensatory strategies (FIM: 30→99)4).
Treatment of the underlying disease is the highest priority.
In adult GS, partial improvement over time is possible, but evidence is limited. In developmental GS (children), the prognosis may be less favorable. Reversible prognosis is expected only when caused by treatable conditions such as tumors or autoimmune encephalitis.
Occupational therapy and speech therapy are central. The use of alternative methods for writing and calculation (e.g., calculators, word processors) is also effective. In post-stroke cases, symptoms may persist after 4 months, but there are reports of significant improvement in functional independence measure (FIM) through the acquisition of compensatory strategies4).
Regarding the pathogenesis of GS, two hypotheses—the classical cortical lesion hypothesis and the more recent disconnection syndrome hypothesis—are discussed in opposition and complementarity.
Cortical Lesion Hypothesis
Proponent: Josef Gerstmann himself proposed it as a “Grundstörung” (common psychoneurological basis)1).
Mechanism: Damage to the cortex of the dominant hemisphere’s inferior parietal lobule, including the angular gyrus (Brodmann area 39), results in loss of the foundational function common to the tetrad.
Issue: A single cortical functional area common to the tetrad has not been confirmed even by fMRI1).
Disconnection Syndrome Hypothesis
Concept: Disruption of white matter tracts connecting the parietal lobe to other brain regions, rather than the cortex itself, causes GS.
Evidence: Even with only 1.7% damage to the angular gyrus, GS developed due to disconnection of the SLF, arcuate fasciculus, and posterior corpus callosum4). Rusconi et al. found a common region within the parietal white matter via fiber tracking from cortical activity foci of four tasks in healthy subjects’ fMRI1).
Supporting Evidence: Decreased FA values on DTI (left SLF and corpus callosum C5 more than 3 SD above control group)1).
The white matter tracts involved in GS are as follows:
Yoon et al. (2023) analyzed a case of Gerstmann syndrome after left parieto-occipital hemorrhage using DTI and identified disruption of the left SLF, MdLF, U-fibers, and posterior corpus callosum (C5). FA values in the left SLF and posterior corpus callosum C5 were more than 3 SD below those of controls, supporting the hypothesis that Gerstmann syndrome is a disconnection syndrome 1).
Vaddiparti et al. (2021) identified functional localization of each of the four signs using cortical electrical stimulation (ECS) in a 32-year-old woman with refractory epilepsy: acalculia = superior parietal lobule + supramarginal gyrus/upper angular gyrus; agraphia = superior parietal lobule; left-right disorientation = upper angular gyrus; finger agnosia = angular gyrus + lower superior parietal lobule. The four signs intersected at the lower superior parietal lobule, indicating minimal overlap at the cortical level 3).
This result indicates that the four signs are localized not to a single cortical region centered on the angular gyrus, but to multiple cortical regions that share the lower part of the superior parietal lobule. This may provide a neuroanatomical explanation for why incomplete GS is common.
Classically, damage to the angular gyrus (Brodmann area 39) of the dominant hemisphere is considered the cause, and it has also been called “angular gyrus syndrome.” However, recent studies have shown that GS can occur due to disconnection of white matter tracts such as the superior longitudinal fasciculus (SLF) and the posterior corpus callosum even with minor angular gyrus damage 4), and the disconnection syndrome hypothesis has become mainstream.
Advances in DTI technology are revealing in detail the role of white matter tracts in the development of Gerstmann syndrome.
Bertagnoli et al. (2025) longitudinally evaluated a case (62-year-old male) of Gerstmann syndrome plus limb-kinetic apraxia after left hemisphere stroke at 2 and 4 months. The lesion extended from the inferior parietal cortex to the superior parietal cortex, precuneus, and perirolandic area, with only 1.7% involvement of the angular gyrus. Disconnection maps revealed disruption of SLF I, II, III, the arcuate fasciculus, and the posterior corpus callosum, suggesting that the four Gerstmann signs and apraxia can co-occur due to disconnection of the frontoparietal network (three branches of the SLF)4).
Functional mapping using ECS identifies the individual localization of each sign and explains the neuroanatomical basis for incomplete forms of Gerstmann syndrome. In the case by Vaddiparti et al. (2021), a patient with Gerstmann syndrome received implantation of a responsive neurostimulation (RNS) device. Because the epileptic focus overlapped with functional areas, resection was not possible, and RNS was chosen3).
Sugiyama et al. (2021) reported a case of encephalitis (36-year-old woman) positive for both anti-NMDA receptor and anti-α-enolase NH2-terminal (NAE) antibodies, in which GS appeared as the initial symptom. MRI showed no clear lesions, but IMP-SPECT confirmed hypoperfusion in the left hemisphere. Complete recovery (MMSE 30/30) was achieved with immunotherapy (IVMP, plasma exchange, cyclophosphamide)5).
Recognition that GS can be an initial symptom of anti-NMDA receptor encephalitis is spreading. The usefulness of functional imaging such as SPECT is suggested even when MRI shows no clear lesions.
