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Table of Contents    
Year : 2014  |  Volume : 62  |  Issue : 2  |  Page : 212-213

"Face of the giant panda with bright eyes" in metronidazole neurotoxicity

Department of Neurology, King George's Medical University, Lucknow, Uttar Pradesh, India

Date of Submission23-Feb-2014
Date of Decision18-Mar-2014
Date of Acceptance08-Apr-2014
Date of Web Publication14-May-2014

Correspondence Address:
Hardeep Singh Malhotra
Department of Neurology, King George's Medical University, Lucknow, Uttar Pradesh
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0028-3886.132424

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How to cite this article:
Chaudhari TS, Malhotra HS, Garg RK. "Face of the giant panda with bright eyes" in metronidazole neurotoxicity. Neurol India 2014;62:212-3

How to cite this URL:
Chaudhari TS, Malhotra HS, Garg RK. "Face of the giant panda with bright eyes" in metronidazole neurotoxicity. Neurol India [serial online] 2014 [cited 2021 Jun 18];62:212-3. Available from:


Metronidazole, a 5-nitroimidazole compound, is often used for prolonged treatment of anaerobic bacterial and protozoal infections including those caused by Entamoeba histolytica, especially in developing countries. Metronidazole induced encephalopathy (MIE) is one of the rare adverse neurological effects associated with metronidazole therapy. Herein, we share our experience of unusual neuro-imaging features encountered in this rare condition.

A 52-year-old man, on oral metronidazole (cumulative dose: 144 g over 4 months) for amoebic liver abscess, presented with acute onset slurring of speech and gait imbalance of 7 days duration. Neurological examination revealed slurred speech, truncal, and appendicular ataxia. Work-up revealed hemoglobin of 10.8 g/dL and elevated alkaline phosphatase (174 U/L). Brain magnetic resonance imaging (MRI) revealed hyperintense signals involving red nuclei and periaqueductal gray simulating "face of the giant panda with bright eyes," [Figure 1]a-c besides signal intensity changes in the cerebellar dentate and inferior olivary nuclei in the medulla [Figure 1]e-g; no changes were observed in the abducens or vestibular nuclei. The signals were iso- to hyper-intense on apparent diffusion coefficient sequence [Figure 1]d,h. Mild rubral tremors remained at 14 weeks of follow-up.
Figure 1: Brain magnetic resonance imaging depicts hyperintense signals in the red nuclei (curved arrows) and the peri-aqueductal gray on T2- weighted (a), fluid-attenuated inversion recovery (FLAIR) (b), and diffusion-weighted sequences (c) resembling "face of the giant panda with bright eyes". Hyperintense signals characteristic of metronidazole neurotoxicity are evident in the cerebellar dentate nuclei (straight arrows) on T2-weighted (e), FLAIR (f), and diffusion-weighted sequences (g). The signals are iso-to hyperintense on apparent diffusion coefficient sequence (d and h). Inset shows an image of the giant panda (L) and its inverted layout (R) for comparison

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Metronidazole therapy, especially long-term, is associated with a wide spectrum of neurologic adverse effects such as encephalopathy, seizures, cerebellar toxicity and peripheral and autonomic neuropathy. The mechanism of metronidazole induced neurotoxicity is not well-understood. Reversible radical-anion injury and γ-aminobutyric acid modulation, as evidenced by follow-up imaging after discontinuation of metronidazole, have been suggested as possible pathophysiological mechanisms. [1],[2] Brain MRI in MIE typically reveals involvement of cerebellar dentate nuclei (most commonly affected site), midbrain (tectum, tegmentum, red nuclei), pons (vestibular and abducens nuclei, superior olivary nucleus in lower pons), medulla (inferior olivary nucleus, dorsal medulla), corpus callosum (in the region of splenium) and subcortical white matter. These changes exhibit characteristic diffusion abnormalities according to the site of lesion. Previous studies have revealed that vasogenic edema predominates in cerebellar, midbrain and brainstem lesions, whereas cytotoxic edema prevails at supratentorial sites such as the corpus callosum and subcortical white matter. [3]

The neuroimaging features in our patient corroborated with those mentioned in the literature. The peculiar feature about this case was the involvement of the red nuclei simulating "bright eyes" of "face of the giant panda." An analogy to the "face of the giant panda" sign previously observed in Wilson's disease is drawn here, though with bright eyes, which to the best of our knowledge has not been described earlier in patients with MIE. We feel that metronidazole neurotoxicity may be added to the list of causes depicting such similarities. [4],[5]

  References Top

1.Rao DN, Mason RP. Generation of nitro radical anions of some 5-nitrofurans, 2- and 5-nitroimidazoles by norepinephrine, dopamine, and serotonin. A possible mechanism for neurotoxicity caused by nitroheterocyclic drugs. J Biol Chem 1987;262:11731-6.  Back to cited text no. 1
2.Evans J, Levesque D, Knowles K, Longshore R, Plummer S. Diazepam as a treatment for metronidazole toxicosis in dogs: A retrospective study of 21 cases. J Vet Intern Med 2003;17:304-10.  Back to cited text no. 2
3.Kim E, Na DG, Kim EY, Kim JH, Son KR, Chang KH. MR imaging of metronidazole-induced encephalopathy: Lesion distribution and diffusion-weighted imaging findings. AJNR Am J Neuroradiol 2007;28:1652-8.  Back to cited text no. 3
4.Hitoshi S, Iwata M, Yoshikawa K. Mid-brain pathology of Wilson′s disease: MRI analysis of three cases. J Neurol Neurosurg Psychiatry 1991;54:624-6.  Back to cited text no. 4
5.Kallollimath P, Nagappa M, Sinha S, Saini J, Bindu PS, Taly AB. Panda with "Bright eyes" in Wilson′s disease. Neurol India 2013;61:100-1.  Back to cited text no. 5
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1 Metronidazole
Reactions Weekly. 2014; 1507(1): 22
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