Mystery Case: Parietal lobe epilepsy with ictal manifestation of Gerstmann syndrome

Pearls

• Gerstmann syndrome, comprising finger agnosia, right–left disorientation, dysgraphia, and dyscalculia, is an uncommon manifestation of epileptic seizures. These signs can be easily overlooked unless tested specifically.

• A careful clinical testing of ictal symptoms can contribute to revealing unnoticed negative symptoms, and eventually the diagnosis and localization of epileptic foci.

Oy-sters

• Manifestation of negative symptoms such as Gerstmann syndrome during a seizure can present diagnostic pitfalls.

• Although positive symptoms such as automatisms, hand dystonia, myoclonic jerking, or tonic-clonic movements are common and well-known ictal signs, negative symptoms should not preclude epileptic seizures. For instance, a loss of ability to write or right–left confusion may be signs of a seizure, instead of a vascular event such as a TIA or stroke.

A 65-year-old right-handed woman of normal development started to experience episodes of right hand apraxia that could last for minutes to hours. She was aware during these episodes and was able to recall the episodes later. Episodes of apraxia that she described include sudden transient inability to turn the steaks that she was cooking on a pan and had to turn off the fire instead, inability to use and to release a knife that she was holding in her right hand and had to use her left hand to help release her right fingers off the knife, and inability to hang clothes on a clothesline. She consulted our epilepsy center when she was 71 years old for the increased frequency of her episodes to a weekly basis, despite treatment with multiple antiepileptic medications (carbamazepine 800 mg/day, lamotrigine 200 mg/day, and zonisamide 400 mg/day). Continuous video-EEG monitoring revealed occasional slowing over the left centro-parietal region without a definite interictal epileptic discharge. During interictal periods, she scored full on the Mini-Mental State Examination, indicative of normal cognitive function, and her neurologic examination was normal. The examination included asking her to say her own name, orientation of place and time, to raise both arms or legs, to move fingers randomly (mimicking piano playing), to distinguish difference in soft touch on each side of her body (for detecting possible sensory deficit), to name objects, to repeat words or short sentences, to write a sentence, to calculate, to imitate meaningless hand gestures, to use tools available at the bedside (such as chopsticks, spoon, pen), to indicate her own body parts under verbal commands (such as right or left index finger, thumbs, toe, leg, nose, mouth), and to recall or recognize objects presented previously. The same examination during an ictal event revealed right hand kinetic apraxia, bilateral ideomotor apraxia, buccofacial apraxia, and Gerstmann syndrome (finger agnosia, right–left disorientation, dysgraphia, and dyscalculia) accompanied by neither aphasia nor impaired awareness. During the event, EEG demonstrated intermixed lateralized rhythmic delta/theta activity over the left fronto-centro-parietal region (figure, A) that waxed and waned for 6 hours and 19 minutes, indicative of a nonconvulsive status epilepticus. These deficits ameliorated with a quick return of the EEG to baseline (figure, B) following an IV injection of 5 mg diazepam, confirming their epileptic nature. Imaging studies revealed hypometabolism in the left supramarginal and angular gyrus on interictal FDG-PET (figure, C) without a definite structural abnormality on MRI (figure, D). Based on the ictal symptoms and the FDG-PET findings, we concluded that the epileptic focus is located within the eloquent cortex and the patient is not a good candidate for surgical resection. Since responsive neurostimulator is yet to be approved in our country, the best option is to offer further optimization of antiepileptic medications or implantation of a vagal nerve stimulator.

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Figure EEG findings during continuous video-EEG monitoring and neuroimaging findings

EEG during one of the nonconvulsive status epilepticus episodes shows an intermixed lateralized rhythmic delta/theta activity over the left fronto-centro-parietal region (A) and following an IV injection of 5 mg diazepam (B) in average montage. (C) Interictal FDG-PET (overlaid on coregistered MRI) revealed hypometabolism in the left supramarginal and angular gyrus. (D) MRI reveals no apparent structural abnormality (only the T2-weighted fluid-attenuated inversion recovery is shown here).

Mystery Case responses: A 71-year-old woman with an unusual case of apraxia

The Mystery Case series was initiated by the Neurology® Resident & Fellow Section to develop the clinical reasoning skills of trainees. Residency programs, medical student preceptors, and individuals were invited to use this Mystery Case as an educational tool. Responses to multiple choice questions formulated using this case were solicited through a group email sent to the American Academy of Neurology Consortium of Neurology Residents and Fellows and through social media. We received 313 responses, 73% from outside the United States. The majority of respondents (67%) had been in practice for 1–4 years; 52% were residents or fellows while 36% were faculty/board-certified physicians; the remainder were medical students or advanced practice providers. A wide range of practice settings were represented.

The 71-year-old patient presented with a 6-year history of discrete episodes of acute-onset right hand apraxia, namely finger agnosia, right–left disorientation, dysgraphia, and dyscalculia. Eighty-nine percent of respondents correctly identified this as Gerstmann syndrome. On reviewing the ictal EEG, 80% of respondents correctly identified lateralized rhythmic delta/theta activity over the left fronto-temporo-centro-parietal region, the likely symptomatogenic zone in this case. An FDG-PET scan demonstrated hypometabolism in the left supramarginal and angular gyri, which was correctly identified by 71% of respondents.

The final question was a test of functional neuroanatomy and 49% of respondents identified the only incorrectly matched ictal symptom and symptomatogenic zone pair; Gerstmann syndrome is caused by dysfunction to the dominant, not nondominant parietal lobe. The most frequent incorrect answer (16%) was hand dystonias and automatisms, which can be localized to the temporal lobe ipsilateral to the automatisms and contralateral to the hand dystonia.^1,2

This case emphasizes the importance of a careful clinical history and examination of patients presenting with seizures in order to localize the symptomatogenic zone in the absence of structural abnormalities. This is a key contribution of a neurologist to the epilepsy multidisciplinary team in presurgical evaluation. The case also serves as an important reminder that seizures can manifest with negative symptoms, which can be as localizing as the more common positive symptoms, such as hand dystonias or ictal pouting.

Robert Hurford, MSc, MRCP (UK)

Nuffield Department of Clinical Neurosciences, University of Oxford