Blink Reflex Usefulness in Acute Phase of Bickerstaff's Brainstem Encephalitis

Bickerstaff’s brainstem encephalitis (BBE) is a Fisher Syndrome (FS) related disorder characterized by the disturbance of consciousness or hyperreflexia in addition to the classical triad of ataxia, areflexia and ophthalmoplegia. The pathophysiology of BBE remains controversial therefore a complete neurophysiological study including the study of cranial nerves may be crucial to add evidence of peripheral or central nervous system involvement in the assessment of patients. We report the case of 29 years old woman with BBE and the blink reflex (BR) follow up studies revealing a correlation between clinical and electrophysiological improvement. This case may support the usefulness of BR studies for electrophisiological diagnosis in BBE in early stages.


Introduction
Fisher syndrome (FS) is characterized by the triad of ataxia, areflexia and ophthalmoplegia, with minimal if any limb weakness. Bickerstaff's brainstem encephalitis (BBE) is a related disorder characterized by the disturbance of consciousness or hyper reflexia in addition to the classical triad and share with FS the association with anti-GQ1b antibodies [1][2][3]. The pathophysiology and the main lesion site in BBE is a matter of debate. Most authors describe a variable involvement of the peripheral and central nervous systems (PNS and CNS) in FS and BBE suggesting a continuous spectrum of disease between them [3][4][5]. Performing early and serial neurophysiological studies would be crucial in establishing the underlying pathology in both entities [6,7]. Specifically, the inclusion of study of facial nerve and Blink reflex (BR) in the neurophysiological study performed may add evidence of peripheral or central nervous system involvement useful to support the diagnosis, especially in its early stages [7].
We present a case of BBE with very early blink reflex electrophysiological findings that were crucial for explaining the physiopathology of the disease and can help with its topographic diagnosis.

Case Report
A 29 years old and previously healthy woman was admitted to neurology department because of a 24 h evolution of gait disturbance, diplopia and numbness in hands and feet. Four weeks ago, the patient presented diarrhoea and abdominal pain for 3 days. General examination revealed 39°C axillar temperatures. Neurological examination (Day 1 after onset) showed consciousness disturbance (she was drowsy but able to respond to commands), complete external ophtalmoplegia, her pupils were equal and with no response to photomotor reflex, bilateral facial palsy, aphonia, discrete left hemiparesis (grade 4+), left babinski, ataxic gait and complete areflexia. Laboratory findings were normal and antibodies against gangliosides (including Gq1b) were negative. Cerebrospinal fluid (CSF) revealed the presence of 70 cells (99% multinuclear cells) with protein and glucose level in the normal range. CSF cultures ruled out other encephalitis aethyologies. Brain MRI did not show any abnormality. Nerve conduction studies (NCS) showed normal compound muscle action potential (CMAP) and distal latencies of all the explored motor nerves (both medians, ulnars and peroneals), blocked F-waves in left peroneal nerve ( Figure 1) and clearly increased latency (61 ms) of R2 compound of right blink reflex (BR) with normal R1 latency (Figure 2a). The patient underwent endovenous immunoglobulin treatment. In day 8 the patient began improving her external ocular motor motility and right BR revealed a less increased of R2 latency and a minimal increased R1 compound latency (Figure 2b), the other electrophysiological findings were normal, including F-waves of left  A second brain MRI showed gadolinium enhancement in both III and V cranial nerves and no brainstem abnormality (Figure 3). Blink reflex was normal (Figure 2c) and NCS reveals a decreased CMAP of facial nerve, the other NCS and F-waves studies were normal. No abnormalities were found at any moment in needle electromyographic studies.
In day 28, she was discharged from the hospital with mild ophtalmoparesis and facial nerve palsy, generalized arefexia and no gait disturbance. In day 70 neurological examinations was normal and NCS did not show any abnormality.

Discussion
This case shows the typical BBE clinical findings areflexia, ataxia, ophalmoparesis and central nervous system signs involvement (left pyramidal signs and consciousness disturbance) associated to pleocytosis in CSF. The electrophysiological findings suggest both peripheral (F-waves block and facial CMAP decreased) and central (increased right R2 latency with normal R1 latency) nervous system involvement. The brain MRI findings suggest an inflammatory process in III and V cranial nerves added. Antibodies against ganglioside Gq1b were negatives, and this can occur in 30% of BBE [3].

Discussion
In our patient the presence of increased R2 latency despite normal R1 during the ophtalmoparesis consistent with a laterobulbar brainstem involvement, helping to add evidence of central nervous system involvement for the diagnossis of BBE in early evaluation and with normal CNS imaging. Ogawara et al. described a case of BBEwith positive antibodies against Gq1b antibodies and absence of R2 compound in blink reflex in day 6 of initial clinics, suggesting nervous system involvement [5]. This absence was transient and blink reflex was normal in day 40.
Serial studies of our patient, showed a normalization of BR study in correlation with clinical improvement.

Conclusion
This case report supports the usefulness of cranial nerve studies including BR in the understanding of the BBE's pathophysiology and diagnosis, especially in very early stages, and also during the evolution of the disease.