Late Blink Reflex Abnormality in a Patient with Dysgeusia: A Case Report

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Introduction

More than 1% of the American is estimated to have taste disorders. Dysgeusia, the distortion of the sense of taste, might be associated with numerous etiologies including glossitis, tooth decay, zinc deficiency, Sjogren syndrome, chemotherapy, and so on. Also, it can be occur as a consequence of stroke attacks.^1-3 Compared

with major stroke clinical features (motor weakness, sensory changes of limbs, dysarthria, aphasia), dysgeusia is thought to be less important because of its little influence on our daily living. Cranial nerves V (trigeminal) and VII (facial), along with their connections in the pons and medulla, can be assessed electrically with the blink reflex. In this case report, we describe a patient with dysgeusia by brainstem infarction which was suspected with blink reflex examination and confirmed with brain magnetic resonance image (MRI). And we discuss the central pathway of the taste and emphasize the importance of unilateral taste impairments and tongue sensory change in stroke patients.

CASE REPORT

ISSN 1229-6066 https://doi.org/10.18214/jkaem.2018.20.2.144 J Korean Assoc EMG Electrodiagn Med 20(2):144-147, 2018

J Korean Assoc

Electrodiagn Med EMG

This is an Open Ac cess article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Received June 22, 2018 Revised August 22, 2018 Accepted October 9, 2018

Corresponding Author: Dong Hwee Kim

Department of Physical Medicine & Rehabilitation, Korea University Ansan Hospital, 123 Jeokgeum-ro, Danwon-gu, Ansan 15355, Korea

Tel: 82-31-412-5330, Fax: 82-31-412-4215, E-mail: [email protected]

미각 이상 환자에서의 후기 눈깜박 반사 검사 이상소견: 증례보고

박홍범, 한아름, 김기훈, 박병규, 김동휘

고려대학교 의과대학 재활의학과

Late Blink Reflex Abnormality in a Patient with Dysgeusia: A Case Report

Hong Bum Park, A Reum Han, Ki Hoon Kim, Byung Kyu Park, Dong Hwee Kim

Department of Physical Medicine & Rehabilitation, Korea University College of Medicine, Seoul, Korea

Although dysgeusia can occur as a consequence of stroke attacks, many physicians and patients tend to overlook it.

A 50-year old woman complained of a 2-week history of abnormal sense of taste on the anterior two-thirds of right tongue. Blink reflex test demonstrated prolonged ipsilateral and contralateral R2 responses with the right supraorbital nerve stimulations, which suggest the lesion on the descending pathway. Brainstem magnetic resonance imaging (MRI) demonstrated abnormal findings in the right lower dorsal pons, anterior to 4th ventricle, lateral to inferior colliculus, and at the level of the pontomedullary junction, which was compatible with solitary tract nucleus and spinal trigeminal nucleus. Brainstem infarction should be considered in patients who have abnormal sense of taste. Additionally, blink reflex test may be helpful for the detection of central origin dysgeusia.

Key Words: blink reflex test, dysgeusia, pontomedullary junction infarction

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Hong Bum Park, et al. Late Blink Reflex Abnormality in a Patient with Dysgeusia

Case Report

A 50-year old woman presented with a 2-week history of abnormal sense of taste on the anterior two- thirds of right tongue and mild hypoesthesia on the right face. She felt only bitter instead of sour, salt, and sweet (Fig. 1). Because of the poor oral intake, she lost her weight by 5 kg within 2 weeks. The right facial weakness was developed and disappeared 1 week later.

She had a history of essential hypertension and multifo- cal infarction in the left middle cerebral artery territory 2 years ago and had only mild weakness (Grade 4) and hypoesthesia on the right upper and lower extremities.

There were no facial weakness, tongue deviation, and extra-ocular movement abnormality. Gag reflex was intact.

Initially, non-enhanced brain MRI and magnetic resonance angiography was performed. However, there were no definite abnormal findings. Two days later, the blink reflex test and needle electromyography (EMG) was performed. The blink reflex test demonstrated prolonged ipsilateral R2 and contralateral R2 responses with the right supraorbital nerve stimulations. The needle EMG findings suggest no trigeminal or facial nerve lesion. Based on the blink reflex test, the lesion on the descending pathway (spinal trigeminal nucleus) was suspected (Table 1, 2). Follow up brainstem MRI was performed after seven days from initial MRI. On T2 weighted images, high signal intensity was observed in the right lower dorsal pons, anterior to 4th ventricle, lateral to inferior colliculus, and at the level of the pontomedullary junction. These lesions were where facial nucleus travels ventrally to exit. And solitary nucleus and spinal trigeminal nucleus were located there (Fig.

2). Solitary nucleus is responsible for taste sensa-

Bitter Sour Salty Sweet

CN IX: general & special sensation Overlapping nerve supply CN V: general sensation CN VII: special sensation

Taste area Innervation

Fig. 1. The illustration of taste area (left) and innervation (right) in the tongue. CN, cranial nerve.

Table 1. Findings of Blink Reflex Test

Supraorbital nerve stimulation

Side R1 response R2 response Contralateral R2 response

Left 11.8 40.7 40.9

Right 11.4 43.6* 44.7*

Asterisk (*) indicates abnormal value. Blink reflex test was performed, which demonstrated prolonged ipsilateral R2 and contralateral R2 responses with the right supraorbital nerve stimulations

Table 2. Findings of Needle Electromyography

Side Muscle Insertional activity Spontaneous activity Motor unit action potentials Recruitment

Rt. Orbicularis oculi Normal - Normal Normal

Orbicularis oris Normal - Normal Normal

Tongue Normal - Normal Normal

Masster Normal - Normal Normal

Needle electromyography was performed. There is no evidence of trigeminal or facial nerve lesion

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tion from anterior two thirds of tongue. Right solitary nucleus, spinal trigeminal nucleus and facial nerve to tongue are involved. The symptoms, which included impairment of general and special sensation on the anterior two thirds of the tongue, coincided well with the findings in the brain MRI and blink reflex test. We diagnosed her as right pontomedullary junction infarction with involvement of solitray nucleus and spinal trigeminal nucleus. Her symptoms gradually improve with oral anti-platelet agent therapy, management of stroke risk factors, and physical therapy. Two months later, dysgeusia in the right tongue disappeared.

Discussion

Many people have experienced a problem with their taste. The most common one is phantom taste percep- tion which is often unpleasant taste even though they have nothing in their mouth. Some people also experi- ence a reduced ability to taste sweet, sour, bitter, and salty, a condition called hypogeusia.¹ And other people cannot detect any tastes, which is called ageusia.

Taste disorders are more common among the stroke patients than we think. However, central mechanism and pathway of the taste are still unclear. The pe-

ripheral taste nerves are facial nerve (chorda tympani nerve), glossopharyngeal nerve, and vagal nerve (great- er petrosal nerve).^1,3,4 These nerves reach the rostral side of the solitary nucleus of the medulla and synapses of these nerves are done.³ These fibers go upward through the inner side of the medial lemniscus or the reticular formation on the same side and pass the pontine taste area in the upper pons.^1-3,5-11 And then, these fibers reach the thalamic subnucleus where neuronal changes are done.^1,3 There are tertiary sensory neurons in the ventral posterior medial nucleus of the thalamus.^1,3,8 Finally, these neurons continue to the inferior margin of the postcentralgyrus, called cortical taste area.^1,12,13

In our case, patient has numbness with taste blind- ness except bitter on the right anterior two thirds of the tongue because her small branch of the facial nerve called the nervus intermedius is damaged by small- sized right pontomedullary junction infarction.^3,14 On admission, although she complained of her hypogeusia we couldn’t find her brain lesion. The size of infarction is too small to be detected by routine MRI protocol of our hospital. We modified the protocol to obtain detailed sections and finally we could understand her symptom’s origin.

CN VI

CN VII

MCP VIII2

ML STT

VII V

VI

ICP VIII1 CST

A B

Fig. 2. Axial T2-weightes MR image shows high signal intensity in the right lower dorsal pons at the level of the pontomedullary junction (A).

The MR image projected onto an illustration (B). The lesion is shown by the dotted line. Right solitary tract nucleus, spinal trigeminal nucleus and facial nerve to tongue are involved. CST: corticospinal tract, ML: medial lemniscus, STT: spinothalamic tract, V: spinal nucleus and tract of trigeminal nerve, VI: nucleus of abducens nerve, VII: motor nucleus of facial nerve, VIII1: ventral and dorsal cochlear nuclei, VIII2: vestibular nuclei, MCP: middle cerebellar peduncle.

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This case supports the results of previous studies about central taste disorders. In our knowledge, there are no reports of dysgeusia associated with abnormal blink reflex. Our study shows pontomedullary lesion can actually affect the blink reflex study. Many studies including our study show that central pathway of taste fibers from the pons to the thalamus has a decussa- tion at the midbrain level. And this pathway continues through a dorsolateral side of the pons.^2,3,7-9 In spite of the known pathway of the taste fibers, the pathways from the pontine taste area to the thalamus are still unclear. Therefore, central taste disorder after stroke should be studied constantly.

Physicians should not ignore any taste disorders because these symptoms can be associated with early stage cerebrovascular disease like our case. Electromy- ography tests, such as blink reflex test, should be considered to diagnose central origin taste disorder.

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