Can you put the clues together to solve this mystery case? It’s a zebra!
A 57 year old, right-handed woman has been previously healthy other than well controlled hyperlipidemia and occasional migraine headaches.
Three weeks ago she developed twitching episodes involving the face and shoulder. These mostly occur on the right side, but occasionally occur on the left side as well. Initially this happened only a few times a day, but has increased in frequency to dozens of times daily. The twitches are brief, and not associated with any alteration of consciousness. While in the hospital she had a single generalized tonic-clonic seizure.
She has become progressively confused, disoriented, and uninhibited. Her MOCA is 21/30, and she was previously a working professional without cognitive complaints.
Her initial brain MRI with and without contrast is notable only for mildly increased bilateral hippocampal T2 signal. An EEG captures the face and arm twitching spells, and is negative for seizures – there is only mild generalized slowing.
Basic labs are notable only for mild hyponatremia with a serum sodium of 130. A lumbar puncture is performed with very mild CSF protein elevation, but no pleiocytosis. HSV PCR is negative on two different occasions.
How do you approach this case? This is a presentation of new seizures in an adult. Generally, new cases of epilepsy present in childhood, and become more frequent again in the elderly due to acquired brain injuries (strokes, tumors, trauma, neurodegenerative disease, etc). For adults with new seizures you should also consider alcohol withdrawal and toxic/metabolic conditions, including benzodiazepine withdrawal.
This patient, however, has a prodrome of progressive confusion leading up to her seizure, as well as frequent jerking episodes of the face & arm. The combination of progressive encephalopathy and abnormal movements leading up to a seizure should make you consider an autoimmune or paraneoplastic condition, such as limbic encephalitis.
Diagnosis: This case is a Zebra, as noted above – the combination of faciobrachial dystonic seizures (which do not have EEG correlate), confusion, and hyponatremia is the classic triad for a condition called LGI-1 limbic encephalitis.