Anti-leucine-rich glioma inactivated 1 (LGI1) encephalitis as a mimic

The patient is 43 years old male with a history of recurrent episodes of speech blockage, left head deviation and pulling sensation to the left side, left upper extremity pilo-erection; Interictal EEG was normal; he was diagnosed as focal epilepsy and was started on levetiracetam, then oxcarbazepine was added due to worsening of his symptoms; the patient later presented to us in status epilepticus with recurrent generalized tonic clonic seizures with no recovery to baseline.

MRI scan with contrast was performed, which demonstrated enlargement and T2/FLAIR hyperintensity of the left amygdala (figure 1), without diffusion restriction or contrast enhancement (figures 2-3).  Bilateral hippocampal hyperintensity and significant atrophy of the left hippocampus were identified (figure 4).

Repeat MRI 6 months post treatment revealed symmetrical amygdalae with normal signal intensity (figure 5).  The hyperintensity of the hippocampi was no longer visible; however the left hippocampus remained atrophic (figure 6).

Background

Autoimmune encephalitis is a collective term for a variety of immune-mediated inflammatory disorders of the central nervous system. Voltage-gated potassium channels [VGKCs] are related to the protein leucine-rich glioma inactivated 1 [LGI1]. LGI1 and VGKCs are co-precipitated by antibodies against LGI1, which are associated with autoimmune encephalitis [1-2]. 

Clinical Perspective

Patients may have seizures, behavioural disturbances, and memory loss with subacute onset [3]. Peripheral signs like neuropathy or autonomic dysfunction frequently coexist but can also happen independently [4]. The FBDS, or faciobrachial dystonic seizure, is defined by frequent [up to 40–50 per day], short, dystonic movements of the ipsilateral face and arm. They are highly suggestive of LGI1 antibody encephalitis.

Imaging Perspective

Imaging wise, LGI1 antibody encephalitis very often demonstrates enlargement and pathological T2 signal of the amygdala, either uni or bilateral.  Mild ill-defined enhancement of the affected amygdala may also occur.  The findings are usually confined within the mesial temporal lobes [5].

Mesial temporal sclerosis develops early in the majority of the patients [5].

These findings may mimic an epileptogenic lesion of the mesial temporal lobes such as a focal cortical dysplasia or a glioma, such as in this case.

Outcome

Corticosteroids and plasmapheresis/ivIG are the management of choice in patients with LGI1 antibody encephalitis.  The long-term outcome is usually favourable.  The most frequent chronic deficit is memory disturbance.

Take Home Message / Teaching Points

In this patient the initial [erroneous] radiological diagnosis was of an epileptogenic lesion of the left amygdala [either focal cortical dysplasia or low grade glioma], causing secondary mesial temporal sclerosis. 

However, the immune panel of the patient later revealed LGI1 antibody encephalitis.

Therefore, it is important for radiologists to be aware of this nosological entity and to include it in the differential diagnosis in patients with seizures and a focal lesion in the amygdala.

Written informed patient consent for publication has been obtained.