An 8-year-old presents to the emergency department following a first seizure episode. They witnessed a generalised tonic-clonic seizure that morning, lasting approximately 60 seconds and remaining post-ictal. They have a history of being non-specifically unwell yesterday with subjective fever, lethargy and a mild headache. They have no significant past medical history and no family history of seizures. The examination is unremarkable. Whilst in the emergency department they have a further two self-terminating generalised tonic-clonic seizures.
Febrile Infection-Related Epilepsy Syndrome (FIRES) is a rare epileptic encephalopathy that results in prolonged refractory status epilepticus in previously well patients.
What are the presenting features of FIRES?
FIRES typically presents in children between the age of 3 to 15 years, with intractable status epilepticus, 2 to 10 days post a febrile illness. The preceding illness is most commonly an upper respiratory tract infection or gastroenteritis. Fevers may have resolved prior to the onset of the acute phase of the condition.
The acute phase of the illness is characterised by frequent seizures, rapidly progressing to status epilepticus. Although the seizures are initially focal in nature, they may evolve into secondary generalised seizures. The acute phase can be prolonged, lasting from weeks to months. An association with rash, liver derangement and arrhythmia has been noted in the literature. There is no latency period.
The chronic phase is denoted by refractory epilepsy, resulting in seizures that may cluster every 2 to 4 weeks. This is often associated with severe neurological impairment and cognitive decline.
FIRES had previously been thought to only occur in children, and New-Onset Refractory Status Epilepticus (NORSE) only in adults, however this theory has been disproven. Although FIRES is more prevalent in children, it has been known to also occur in adults. As such, FIRES is now considered a subtype of NORSE, characterised by a preceding febrile illness. It has previously been known as Acute Encephalitis with Refractory, Bepetitive Partial Seizures (AERRPS) and Devastating Epilepsy in School-age Children (DESC).
The aetiology of FIRES in unknown and as such the pathophysiology remains unclear.
One theory is that FIRES is a form of severe infectious encephalitis, but as yet no infectious agent has been identified, and the refractory nature of the seizures is atypical of encephalitis. Another hypothesis suggests FIRES is the result of an immune response, however, there is not enough evidence to support this theory.
A case identifying anti-GABA A receptor antibodies in the CSF of a patient who presented with severe refractory status epilepticus associated with a fever led to speculation that the condition may be autoimmune-mediated. Again this has not been proven and the case may have been an exception rather than a rule.
Other theories include genetic associations and potential links with metabolic disease, but as yet a cause has not been identified.
Diagnosis and Differentials
The diagnosis of FIRES is essentially clinical, as FIRES is a cryptogenic illness. The work up is initially general, and focused on the exclusion of other treatable causes, such as infectious or autoimmune encephalitis.
A detailed history will identify the preceding febrile illness, and would be focussed on the identification of risk factors for other causes for the presentation, including exposure to animals, drugs and toxins, recent foreign travel and immunosuppression.
Blood sampling will be used to identify an infectious cause for the presentation, through full blood count, blood cultures and a screen for atypical infective agents. Lumbar puncture should be performed for CSF sampling in order to investigate bacterial, viral, fungal or autoimmune causes. CSF may show a mildly elevated white cell count in those with FIRES.
EEGs may show a generalised slowing, in keeping with an encephalopathic picture, but do little in the way of distinguishing between other causes of seizures. However, they are useful in guiding treatment and identifying non-convulsive seizures.
Initial MRI imaging is often normal, however, follow up imaging has been associated with devastating changes. Early MRI, in the first weeks of the acute illness, has shown swelling of the mesial temporal structures and increased T2 weighted signal. Follow up MRI, greater than 6 months after onset, may be associated with bilateral mesial temporal atrophy and increased T2 weighted signal. It should be noted that MRI may be normal in 50% of cases.
Differentials to consider are Dravet Syndrome, which presents with a febrile illness associated with status epilepticus, though this tends to present within the first year of life. Also Alper’s Disease, which presents with refractory seizures in previously well children, and is often associated with liver disease.
The patient is loaded with levetiracetam (40mg/kg) as per hospital guidelines, and admitted under paediatrics locally. A CT head is unremarkable and bloods show mild LFT derangement with normal inflammatory markers. They are treated empirically with intravenous cefotaxime and aciclovir. Later that afternoon they develop a fever of 38.3.
The GCS fluctuates between 11 to 13 with no full recovery to baseline until later that evening. Following two focal seizures the next afternoon, they are transferred to the local tertiary centre for further investigation and management.
Initial management involves treating the seizure, and more often status epilepticus. Local hospitals have their own guideline for managing status epilepticus but the first line is typically benzodiazepines (lorazepam, diazepam, midazolam, clonazepam). Second-line treatment is standard anti-convulsants (levetiracetam, phenytoin, phenobarbitone, sodium valproate), however, FIRES does not typically respond to these medications even in high doses.
The seizure pattern in FIRES is often resistant to multiple anti-epileptics. Alternative treatment options have to be sought although there is limited evidence as to the optimal treatment.
There is limited data on the treatment of FIRES, however, they all conclude the seizures are very difficult to manage and often require polytherapy. Some of the alternative treatment options include drug-induced burst-suppression comas, immunotherapy, a ketogenic diet, vagus nerve stimulation, therapeutic hypothermia and intravenous magnesium sulfate. The most commonly used and researched options are discussed below.
Burst suppression coma
Burst suppression coma induction is viewed as standard care for refractory status epilepticus. If first and second-line treatments fail the next option involves high doses of anti-convulsants along with anaesthetic agents, for example, an infusion of midazolam, barbiturates or propofol. Unfortunately when the anti-convulsants are weaned the seizures tend to reoccur. Prolonged burst suppression coma has been associated with a significantly worse cognitive outcome and poorer prognosis.
Immunotherapy has been trialled due to the suspected role of inflammation in the pathogenesis of FIRES. High dose steroids, intravenous immunoglobulin and plasmapheresis have all been used. There is limited evidence to suggest a beneficial role in the management of refractory epilepsy. A large-scale Japanese study described 2 out of 12 patients responding to steroids, although there is not enough evidence to support this as a treatment option. Treatment with immunotherapy is often associated with significant side effects
Anakinra is a recombinant and modified human interleukin-1 receptor antagonist protein. Recent evidence has shown it to be an effective and promising treatment option in patients with FIRES, though relapse has been reported after withdrawal. It has been shown to decrease the duration of mechanical ventilation and hospital length of stay, and possibly seizure reduction. Future studies are required to understand the optimum dosing regime and safety of anakinra.
A ketogenic diet is a high fat, adequate protein and low carbohydrate diet aimed at imitating the body’s fasting state. The body, therefore, metabolises fat for energy. The early introduction of the ketogenic diet has shown to be beneficial in the management of FIRES in uncontrolled trials. It has been suggested that the ketogenic diet may have an anti-inflammatory, as well as an anti-convulsant effect. Some reports suggest it may also have a positive effect on long term cognition. Currently, it is one of the only management options shown to be effective. Future controlled studies are needed to prove this efficacy.
Vagus nerve stimulation
Vagus nerve stimulation (VNS) involves the implantation of an electrode that produces intermittent electrical stimulation into the left cervical vagus nerve. Case reports have found benefit from VNS in the cessation of seizures in patients with refractory status epilepticus and NORSE. There is limited evidence of its use in FIRES.
Long term effects
The prognosis of FIRES is poor. The outcome varies with the length of the acute phase with mortality rates up to 30%. Of those patients who survive there is 66-100% chance that they will have long term cognitive impairment due to damage of the frontal and temporal lobe functions. Survivors with a normal cognitive function will present with a spectrum of learning disabilities, behavioural disorders, memory issues and sensory changes. There is a high risk of recurrent status epilepticus. Unfortunately, only a tiny proportion of survivors will have no neurologic sequelae.
The patient required a lengthy PICU admission where they were managed with a burst suppression coma, ketogenic diet, high dose steroids and intravenous immunoglobulin.
They were later diagnosed with Febrile-Infection Related Epilepsy Syndrome after extensive investigations, including a normal brain MRI and a lumbar puncture which showed a mildly elevated white cell count but was otherwise unremarkable.
They are currently seizure free on a combination of oral phenobarbitone, perampanel and levetiracetam but have some cognitive sequelae.
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