In 1924 the Austrian neuroscientist Josef Gerstmann described a rare neurological disorder which was observed by him in a few patients consisting of tetrad of symptoms; an impairment in performing calculations (acalculia), discriminating their own fingers (finger agnosia), writing by hands (agraphia) and distinguishing left from right (left-right disorientation).
This syndrome is also described in normal apparently but brain-damaged children, who present with learning disability, where it’s called developmental Gerstmann’s syndrome.
Gerstmann’s syndrome is caused by specific brain lesions which affect the posterior lobule of the parietal lobe in the dominant hemisphere, which is usually in the left hemisphere but in some patients it could be the right , especially the angular gyrus and adjacent structures (at the confluence of parietal, temporal and occipital lobes), some studies showed that it’s caused not only by lesion in the mentioned area but also in the left middle frontal lobe of the dominant hemisphere.
The cause of this syndrome may be from:-
Other diffuse etiologies are:
Other reported cases presented with Gerstmann’s syndrome, like cystic lesions with dilated perivascular spaces, as a complication of cerebral angiography, as a complication of the contrast which is used in angiography, as a complication of endovascular treatment of dural arteriovenous malformation, posterior leukoencephalopathy syndrome, necrotizing granulomatous inflammation of small-medium sized subarachnoid vessels, adverse drug reaction of Acetazolamide and embolism from left atrial myxoma.
Transient symptoms of this syndrome may occur as a result of parietal lobe epilepsy.
Because of the variation of the causes, this syndrome can occur in children, young and elderly patients, where it has been called “developmental Gerstmann’s syndrome” in children.
The symptoms of Gerstmann’s syndrome can be explained by a disorders affecting specific areas of the brain, but some disagreements between the studies about the exact localization of the disease, for an example finger agnosia and acalculia responsible sites were found in the supramarginal gyrus or close to the intraparietal sulcus, and involvement of the superior parietal gyrus was founded to be responsible for agraphia, further studies are needed to know whether the syndrome occurs as a result of angular lesion with or without subcortical extension.
Several hypotheses have been mentioned in order to explain Gerstmann’s syndrome, but none of this hypothesis has been confirmed.
Several authors have suggested the defect which causes some symptoms (acalculia, right-left disorientation, and finger agnosia) of this syndrome is in the mental spatial rotations, it’s thought that the problem in this syndrome is in restricting the degree ’s freedom of spatial rotation; especially defective horizontal mapping.
It is thought also that pure form of Gerstmann’s syndrome is caused by disconnection from a subcortical parietal white matter lesion which affects crossing fiber tracts and disconnects separate cortical networks.
The symptoms of Gerstmann's syndrome should include; finger agnosia, acalculia in which patients understand the numbers but cannot perform a simple addition, left- right disorientation and agraphia, a study suggested that acalculia is always associated with semantic aphasia, which has a significant involvement in the angular gyrus, and the paper suggested that the syndrome should include semantic aphasia instead of agraphia, the later may occur in case of superior parietal gyrus involvement, symptoms of this syndrome may be complete or partial  and may be attributed to other cerebral symptoms and can occur in elderly and children.
This syndrome may be transient and caused as an ictal symptom in partial epilepsy, but it may occur as three symptoms out of 4.
The symptoms and signs of this disease in children may appear late in the years after perinatal asphyxia and may only suffer from other symptoms in the neonatal period; seizures.
Other symptoms and signs which may accompany this syndrome differ according to the cause of this syndrome such as; apraxia, optic ataxia, cognitive decline, numbness or weakness. Gesture imitation defects and toe agnosia may be seen as an association with finger agnosia so it may be named as digit agnosia.
So to diagnose this syndrome a complete history and physical examination should be done to guide the physician toward the cause of it.
Some special neurological examination should be done to diagnose the 4 components of Gerstmann's syndrome;
As the number of Gerstmann’s syndrome component increased the responsible brain lesion tend to be larger
Any patient with the symptoms and signs of Gerstmann’s syndrome should be evaluated by neuroimaging MRI/CT scan, abnormalities should be seen in the dominant angular gyrus with or without the involvement of the surrounding areas, abnormalities that should be seen in the imaging differs according to the cause of the syndrome.
In infarction it may be detected in CT scan as a low-density focus, but also a high-density focus in the parietal lobe has been reported in one patient with Gerstmann’s syndrome, MRI in the acute phase will show an abnormally reduced diffusivity , technetium-99 bicisate single proton emission computed tomography will also show a decreased cerebral blood flow with an increased lactate in MR spectroscopy and slowed waves in the affected hemisphere in electroencephalography, and angiography may show stenosis in the middle cerebral artery.
Studies showed the cerebral blood flow would be decreased in the non-infarcted areas also.
In patients with chronic subdural hematoma computerized tomographic (CT) scan will see an extra-axial hypodense fluid collection
In multiple sclerosis, brain MRI will show plaques in the mentioned areas, and in posterior leukoencephalopathy syndrome, MRI T2-weighted images will show an abnormal high-intensity lesion in the gray and white matter.
In necrotizing granulomatous inflammation will cause a lymphocytic pleocytosis in the cerebrospinal fluid and marked meningeal enhancement on MRI with dilated cortical venules.
Other lesions from other disorders in the parietal lobe may be detected by MRI such as JC virus, the lesions may not be limited to the parietal lobe, but may involve other lobes and other areas.
The differential diagnosis for Gerstmann’s syndrome includes:
Presence of Gerstmann’s syndrome with other disorder can make the normal life impossible, mainly due to the severe light-left disorientation. But children who present with developmental Gerstmann’s syndrome may show an improvement with intensive speech training especially when it's diagnosed early.
As the number of Gerstmann’s syndrome components increase the responsible lesion tend to be larger and the neurological impairment tend to be larger also; every patient with the 4 components of this syndrome is more likely to have severe impairment of brain function and the lesion tend to compromise the survival of the patient.
Patient with Gerstmann’s syndrome may show an excellent recovery after intensive rehabilitation and treatment, but acalculia may have a delay in the recovery. Also, children with developmental Gerstmann’s syndrome may exhibit improvement in the syndrome, but this may require early recognition and diagnosis of the syndrome.
Gerstmann’s is a neurological disorder and there is rising ethical issues with the advancing neuroscience, but overall the potential benefits of applying neuroimaging, psychopharmacology, and neurotechnology to mentally ill and healthy persons have to be carefully weighed against their potential harm.
For patients with Gerstmann’s syndrome coordination between neurologist, psychiatrist, physiotherapist, occupational therapist, home health nurses, and sometimes a neurosurgeon should be applied, in order to get a better outcome. [Level III]