Introduction

Miller Fisher Syndrome (MFS) is an extremely rare nerve disorder related to the Guillain-Barré Syndrome (GBS).¹ GBS is a rare neurological autoimmune disorder in which a person’s immune system attacks part of their nerves that carry signals from the brain and spinal cord to the rest of the body. These nerves then lose their ability to transmit signals efficiently, and the muscles begin to lose their ability to respond to the brain's commands, which causes weakness.²

Similarly, MFS is an autoimmune disease where the immune system attacks the nerves. MFS has an annual incidence of 1 or 2 in 1,000,000 people and can affect people of any age group, i.e., both children and adults can be affected by MFS.⁴ MFS is more common in East Asia, more common in males than females, and in young people than old people. The average age of onset of MFS is 45 years.³

MFS is named after Dr. Charles Miller Fisher, a Canadian neurologist at Massachusetts General Hospital. He described the condition in 1956 in three patients who had three common symptoms of the disorder: eye muscle weakness, lack of coordination, and absent tendon reflexes.³

Overview of MFS

Symptoms

MFS usually manifests with a sudden onset of three key symptoms: ^2,3 

• Difficulty in walking due to abnormal muscle coordination (gait ataxia) 
• Loss of reflexes in the tendons (areflexia) 
• Paralysis or weakness of the eye muscle, which causes difficulty in moving the eyes, and may cause double vision (ophthalmoplegia)
• Weak muscles with some patients may also having weakness in the facial and throat muscles, which impacts swallowing
• Respiratory (breathing) problems or respiratory failure due to a weakness in breathing muscles—these patients are then said to have GBS-MFS overlap

Causes

Although the exact cause of MFS is unclear, it is linked to the presence of specific antibodies (mainly anti-GQ1b).¹ These antibodies that develop after a bacterial or viral infection (especially Campylobacter jejuni, a diarrhoeal illness, or Haemophilus influenzae) sometimes attack the nerves of the individual,i.e., MFS is an autoimmune disorder. These antibodies may attack and destroy the myelin sheath, which insulates and protects the nerve fibres. The antibody is directed against a molecule called ganglioside GQ1b (and hence called anti-GQ1b). The antibody is found in at least 80% of people with MFS and hence is used as a confirmatory diagnosis.³ 

Miller-Fisher Syndrome (MFS) typically does not occur in more than one person within the same family. Although very rare cases have been reported in siblings or identical twins, suggesting a possible genetic predisposition, MFS is not considered an infectious disease.³ 

Disorders with similar symptoms

In rare cases, patients with MFS show only one of its usual symptoms, such as paralysis of eye movements or lack of coordination. MFS sometimes affects the limb and respiratory muscles and is known as MFS-GBS overlap syndrome. Currently, there is no reliable way to predict who will experience this progression, but when it occurs, it usually happens within the first week.³ MFS shares symptoms with Bickerstaff brainstem encephalitis, another condition associated with the same antibodies against ganglioside GQ1b.¹ Bickerstaff brainstem encephalitis is distinguished by additional symptoms, such as altered consciousness and specific reflex changes that indicate central nervous system involvement.³

Diagnostic methods

It is difficult to diagnose MFS because it is rare and can show symptoms similar to other neurological conditions such as myasthenia gravis, encephalitis, basal meningitis, etc. It is important to rule these out and test for the presence of anti-GQ1b antibodies to aid in diagnosis. However, these antibodies are also found in Bickerstaff brainstem encephalitis.³

Diagnosis begins with the symptoms and medical history of the patient. There is no single definitive test for MFS. Testing the cerebrospinal fluid usually shows increased protein levels with a normal cell count (which is also seen in GBS).¹ In contrast, about one-third of Bickerstaff brainstem encephalitis patients show an increased cell count in their cerebrospinal fluid.³ Anti-GQ1b antibodies are often present. Nerve tests like electromyography (EMG) are generally normal. In MFS, motor nerve tests are usually normal, but sensory nerve action potentials may be absent, and abnormalities in sensory nerves related to tendon reflexes can be observed. These tests involve recording the activity of muscles after small electric shocks to the nerves. Magnetic resonance imaging (MRI) of the brain may also be part of the diagnostic process. In MFS, MRIs are generally normal, though the brain stem can show abnormalities in Bickerstaff brainstem encephalitis. In GBS, MRI often shows enhanced signals in the spinal nerve roots after the injection of a contrast dye.³ 

Management and treatment

Most patients with MFS recover within six months without specific treatment, with an average recovery time of 2 to 3 months. Very few patients have lasting neurological issues, and the condition is usually not life-threatening. Relapses occur in less than 3% of patients. MFS generally has a good prognosis, and no clinical trials have been conducted, making it unclear if specific treatments are necessary.³ Mild cases often improve on their own without treatment.¹ However, in some cases, the condition can worsen, and since MFS is related to GBS and may progress to MFS-GBS overlap syndrome, treatments for GBS are often used for MFS. These include immunotherapy with intravenous immunoglobulin (IVIg) or plasmapheresis (plasma exchange), but not steroids, as they are ineffective in GBS.³

The preferred treatment is usually IVIg, which involves infusing high doses of immunoglobulin, which are antibodies from the blood, into a vein daily for five days. The immunoglobulin from the plasma of healthy donors works by blocking the antibodies causing the disease.³

The alternative treatment is plasmapheresis, which removes antibodies directly from the blood. In this, blood is taken from a vein, and the plasma, which contains the antibodies, is separated from the red blood cells. The red blood cells are then returned to the body with a substitute to the plasma. Plasmapheresis is usually performed five times in about two weeks. However, IVIg is preferred as it is more convenient and easily available than plasmapheresis.³ 

Complications

Fatigue is the most common complication of MFS and affects about 75% of the patients. Around 33% of patients feel pain even a year after initial symptoms. Patients who have prolonged stays in the ICU can show severe complications. These complications include sepsis, pneumonia, pulmonary embolism, etc. Additional complications can occur due to autonomic dysfunction, such as arrhythmias. 

A severe complication is respiratory muscle fatigue in ICU patients over the age of 50. It can cause respiratory failure and increase the chances of death. Among severely affected patients, 20% to 33% may be unable to walk for more than six months after the initial symptoms, especially if they were infected with Campylobacter jejuni. Due to ongoing pain and disability, some patients also undergo chronic psychiatric issues.⁴ 

Prevention

There is no guaranteed way to prevent MFS. Since MFS is often initiated by bacterial and viral infections, one should take steps to reduce the risk of microbial infections, which in turn helps lower the chances of developing MFS. Below are some preventive measures: ^{4, 5}

• It is important to have good hygiene practices during food preparation, such as washing hands with soap and water, especially before and after handling raw meat, and ensuring that all meat products are cooked to kill harmful bacteria
• Using clean water for drinking and cooking to prevent waterborne infections
• Drinking pasteurised milk to avoid exposure to harmful bacteria
• Practising safe sex to reduce the risk of sexually transmitted infections that could trigger MFS
• Immunocompromised people should follow their prescribed medication to reduce the risk of infections that could cause MFS 

Summary

Miller Fisher Syndrome (MFS) is a rare variant of Guillain-Barré Syndrome (GBS). Both of these are neurological conditions that cause muscle weakness. MFS usually arises when the immune system mistakenly attacks nerve proteins essential for movement and sensation, often following bacterial or viral infections. The most common bacterial cause is Campylobacter jejuni, while viral causes include HIV. Symptoms of MFS are muscle weakness, especially in the eyes and face, difficulty in walking, numbness in the hands and legs, and coordination problems. Diagnosis includes clinical evaluation, antibody testing, nerve conduction studies, and imaging to rule out other similar conditions. 

Treatment for MFS is similar to GBS and focuses on managing symptoms. Hospitalisation may be needed to monitor in severe cases where respiratory function is impacted. Treatments like injection of immunoglobulin and plasma exchange help reduce the attack on the nerves by the immune system. MFS usually resolves by itself in a few weeks to months. Most patients recover fully and experience no long-term muscle weakness. Preventing MFS includes reducing exposure to bacterial and viral causes by following good hygiene practices, like washing hands, hygienic food preparation, disinfecting water supplies, and practising safe sex. While MFS is difficult to prevent completely, these measures can help reduce the risk of the infections that may lead to the syndrome.