The catastrophe of rabies encephalitis: A case series

INTRODUCTION

Rabies is a neurotropic viral illness that follows infection by a family of rhabdovirus. Human rabies, though rare in developed nation, continues to be a major problem in developing nations like ours. It is transmitted from an animal bite, usually following a dog bite, and travels to the central nervous system (CNS) trans-synaptically. Human rabies presents in encephalitis or paralytic form and is nearly always fatal. The literature on neuroimaging features in human rabies infection is scarce, due to its fulminant course. We present imaging features of two cases of rabies encephalitis who presented with an encephalitic form of rabies.

CASE 1

A 22-year-old female with a history of dog bite over the dorsal aspect of the right wrist 7 days back was brought to the emergency department with disorientation, altered sensorium, and irrelevant talks since the morning of that day. She had fever for the past 4 days and had difficulty swallowing water and breathing on the day of admission. On examination, Glasgow Coma Scale (GCS) was E3V2M5 on the day of admission, that is, a total score of 10, meaning she had a lack of spontaneous eye opening; however, eye-opening in response to the speech was present, the verbal response was found to be incomprehensible, inability to exhibit movements in response to a command was found; however, she was able to respond to focal painful stimulus and localize its site. The family provided an account of her receiving three doses of post-exposure prophylaxis injections after the bite, the details of which were not available, as family members did not have any medical documents or records for the same. A computed tomography (CT scan) of the head performed on the day of admission was normal. A cerebrospinal fluid (CSF) obtained from a lumbar puncture demonstrated significantly elevated proteins (506 mg/dL). CSF glucose was within normal limits. Blood examination revealed elevated counts and inflammatory markers. No organism growth was found in the blood culture. Eventually, she developed progressive hydrophobia and photophobia.

Magnetic resonance imaging (MRI) of the brain [Figure 1] revealed symmetrical T2/fluid-attenuated inversion recovery (FLAIR) hyperintensities in bilateral basal ganglia, dorsal aspects of the midbrain, pons, medulla, and visualized cervical cord. Abnormal T2 hyperintensity was also noted in internal and external capsules, mimicking the lentiform fork sign. There was no noticeable post-contrast enhancement. Given the clinical history and physical examination findings, MRI features were consistent with rabies encephalitis. Biopsy samples obtained from the skin of the nape of the neck revealed perivascular lymphocytic inflammation. The patient was managed conservatively in the intensive care unit (ICU). Her condition rapidly deteriorated over the next 2 days with progressively increased oxygen requirement. She also developed acute kidney injury. There was a fulminant progression, and the patient succumbed to non-responsive metabolic acidosis.

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Figure 1:

Case 1 – The axial T2 images (a-c) shows symmetrical hyperintensity in the basal ganglia, the dorsomedial thalami, bilateral mesial temporal region (uncus and amygdala), the basifrontal region, midbrain, the pontine tegmentum, medulla, and the cervical cord. Involvement of bilateral dentate hilus was also evident. The diffusion images (d and e) were negative for any restriction. (f) No abnormal blooming noted in the susceptibility-weighted images. The sagittal fluid-attenuated inversion recovery image (g) showed the diffuse brainstem and cervical cord involvement.

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CASE 2

A 15-year-old right-handed adolescent was brought to the emergency room with a history of altered sensorium for the past 3 days. He was intubated in the district hospital and shifted to our hospital. There was a history of a bite by a street dog with evidence of a level 4 bite over the right leg 15 days back. The patient’s family provided a history of agitation and irritability, which started 8–9 days after the dog bite; however, they denied noticing hydrophobia-like symptoms. There was no antecedent history of fever, convulsion, or psychosis. The family was not able to trace the status of the dog. On examination, GCS was E2VtM5 (without sedation) and plantars were equivocal. Imaging revealed T2/FLAIR hyperintensity in the bilateral basal ganglia, posteromedial aspect of bilateral thalami dorsal aspect of the midbrain, pons, and medulla, cervical cord. The internal capsule, external capsule, corona radiata, and centrum semiovale also appeared hyperintense [Figure 2]. Clinical suspicion of rabies encephalitis was made and managed conservatively in the ICU isolation room. Family deferred lumbar puncture and nuchal skin biopsy. However, due to rapid clinical deterioration, the patient died after 4–5 days of admission. Family members denied brain autopsy.

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Figure 2:

Case 2 – The axial T2 images (a and b) shows symmetrical hyperintensity in the basal ganglia, the dorsomedial thalami and the pontine. The sagittal T2 image (c) showed contiguous involvement of the medulla and adjacent cervicomedullary junction.

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DISCUSSION

The term “rabies” originates from the Latin word rabere, meaning rage, and is also derived from the Sanskrit word rabhas, meaning “the act of violence” to do violence.^[1] Rabies, also known as hydrophobia or aquifuge, is a zoonotic disease caused by rabies virus, a type of ribonucleic acid virus of the rhabdovirus family.^[2-4] Even though preventable by timely vaccination, it is nearly always fatal after the onset of symptoms. It spreads to humans through the infected saliva of wild and domestic animals, the most common culprit being non-vaccinated rabid dogs. Other unusual modes of infection are transmission through organ transplantation and aerosols.^[5] Numerous deaths occur yearly due to rabies, predominantly in Asia and Africa. Most patients (40%) bitten by rabid animals are <15 years of age.^[6]

The World Health Organization has classified exposure into three categories depending on the severity and risk of progression: Category I: Touching or feeding animals and animal licks on intact skin (no exposure); Category II: Nibbling of uncovered skin, minor scratches, or abrasions without bleeding (exposure); and Category III: Single or multiple transdermal bites or scratches, contamination of mucous membrane, or broken skin with saliva (severe exposure).^[7]

Human rabies presents in encephalitic and paralytic forms, the former being more common.^[8] Rabies encephalitis presents as an acute CNS infection. The brainstem and cerebrum are the most common parts of the brain affected; however, the cortex is relatively spared. The early localization of the virus in the limbic system correlated with these patients’ emotional and early behavioral changes. Similarly, cortical sparing correlates with the fact that the affected person is alert and cognitively intact.^[2,3]

Patients with rabies encephalitis present with hyperactivity that rapidly escalates into episodes of fluctuating consciousness. Hallmark features of rabies encephalitis are phobic spasms, aerophobia, and hydrophobia, triggered by puffs of air and sounds or even the mention of water.^[8] Routine CSF examination shows elevated CSF protein levels. The medulla and spinal cord are primarily involved in paralytic rabies.^[2]

CONCLUSION

MRI, in the presence of appropriate clinical history, has the potential to diagnose rabies encephalitis due to unique imaging features. It can also distinguish rabies encephalitis from other close differentials.

TEACHING POINTS

1. Involvement of the dorsal aspect of the brainstem, along with bilaterally symmetrical involvement of the limbic system, basal, and thalami, with the absence of hemorrhagic changes, is a hallmark feature of rabies encephalitis.

2. Involvement of the spinal cord can be seen in encephalitis and paralytic forms; however, more common in the latter.