Have you been told that the muscle stiffness and intermittent paralysis your child experiences are a congenital disease that has no cure? Well, while paramyotonia congenita(PMC) is exclusively managed with drugs to alleviate symptoms, there are, however, evidence-based non-drug approaches that can help patients reduce symptoms. This article explores various lifestyle modifications that you can adopt to help your child with PMC manage their symptoms better and live normal lives. 

Introduction

Paramyotonia Congenita is a rare congenital disease with an unknown prevalence, but it is estimated to affect less than 1 in 100,000 people in Europe. The term was first used by von Eulenburg in 1886 and recognised as the first temperature-sensitive conditions in humans.^1,2 PMC occurs as a result of a missense mutation in the SCN4A gene in foetal development, leading to hypersensitivity of the sodium channel and involuntary muscle contraction.¹ The symptoms of

 PMC usually appears in early childhood and affects muscles in the face, tongue, and hands more than those in the legs ¹.  Known as a paradoxical condition because its symptoms worsen with physical activity, PMC symptoms can also be exacerbated by diets, temperature and hormones.¹

What is paramyotonia congenita

PMC is a rare genetic disorder that is characterised by an inability of the skeletal muscles to relax after contraction, leading to stiffness and, in some patients,  mild paralysis that is mostly paroxysmal.³ This defect is a result of a mutation at the SCN4A gene, which codes for the alpha subunit of the voltage-gated sodium channel  Nav1.4 in skeletal muscle.³ The result of this is reactivation of the sodium channel instead of the normal repolarisation that follows a contraction.  Hence, instead of the muscles relaxing after contracting, another stimulus for contraction is sent to the brain, so the skeletal muscle remains contracted, resulting in muscle stiffness.  PMC is hereditary, and only one copy of the defective gene is needed for individuals to express the defect.⁴ Therefore, offsprings of parents with PMC 

has a 50% chance of having the defect. While PMC results in skeletal muscle stiffness and weakness, it does not result in muscle wasting.³ Therefore, muscle mass is maintained in patients with this defect, such that it is difficult to notice anything abnormal in them except when they have an active episode.

Symptoms of paramyotonia congenita 

The most prominent symptoms of PMC are myotonia, which is characterised by delayed muscle relaxation, leading to muscle stiffness and paralysis.⁵ As a matter of fact,  research has shown that the presence of paralysis distinguishes PMC from another type of myotonia disease known as Thomsen’s disease.⁶ Most people report that during an episode, they experience involuntary muscular movement, such as:

• The clenching of a fist
• Inability to recontour the face after smiling or sneezing
• Difficulty in chewing and swallowing
• Muscle cramps and pain
• Difficulty with speech
• Difficulty in opening the eyelids 
• Paralysis, which can affect limbs separately or all at once. 

These symptoms are usually triggered by cold environments, such as during winter, cold water or drinks and cold air. Sometimes the stiffness can be localised or extensive, depending on the extent of the exposure to cold.6 In addition, repetitive movements or physical activities can trigger or worsen these symptoms, as well as fasting and certain hormonal conditions (menstruation, pregnancy, for example).¹

Local cooling effect on a PMC patient. After the right eye was cooled for 10 minutes And the asked to forcefully close both eyes in the left image and open them in the right image, with the right eye still involuntarily closed.¹¹

Diagnosis of paramyotonia congenita

 The diagnosis of PMC is done by a combination of clinical history, family history, physical exam, electromyographic and genetic tests. Electromyographic test records myotonic activities and reveals the specific muscle experiencing excitability abnormalities during a provocative exposure, such as cold or repetitive activities.¹ However, since several other conditions result in myotonia, such as  Thomensen’s disease and dystrophia myotonica, it is therefore crucial for a differential diagnosis of PMC.⁵ PMC is distinguished mainly by its clinical presentations, including cold sensitivity leading to muscle stiffness that is followed by muscle paralysis, which worsens with repeated muscle activity.⁷ Therefore, observing the clinical presentation is crucial before giving a conclusive diagnosis for PMC, as other myotonic diseases mimic PMC. Genetic testing is used to make a confirmatory diagnosis for PMC, as it reveals the mutation in the SCN4A gene.⁹

Treatment of PMC

While PMC has no cure, certain drugs can be administered to alleviate symptoms and improve patients' quality of life. Sodium channel blockers  have been found to relieve symptoms of muscle stiffness:⁸

• Mexiletine 
• Carbamazepine
• Procainamide
• Phenytoin

Also, tricyclic antidepressants have shown great treatment potential, including:

• Clomipramine 
• Imipramine

Other drug treatments for muscle stiffness and paralysis include:

• Benzodiazepines
• Calcium antagonists
• Taurine 
• Prednisone
• Acetazolamide

These drugs help to relax muscles by blocking sodium channels from excitability, and they also alleviate paralysis. PMC is non-life-threatening and non-progressive and has a good prognosis; however, the disability that results from symptoms can affect a person’s quality of life mentally and socially. Hence, these drugs can reduce symptoms and enhance quality of life.¹

Non-drug management of paramyotonia congenita

While drugs have proven effective in managing symptoms, certain non-drug strategies can be adopted to reduce the occurrence of symptoms. These approaches, if effectively adhered to, can reduce the number of times individuals have an active episode and help symptoms reverse faster if already occurred. These approaches include:

Temperature regulation  

PMC is a temperature-sensitive condition; this implies that when exposed to cold temperatures, myotonia occurs. Therefore, patients with these conditions can reduce the occurrence or severity of myotonia by maintaining a warm environment.

This includes:

• Wearing warm clothes
• Warm shoes to protect the feet
• Drinking and eating warm fluids and foods
• Bathing with warm water 
• Ensuring windows and doors are closed always
• And during winter, utilising a heater to ensure a warm environment

Stress reduction 

Stress triggers myotonia; managing stress and strenuous activities will worsen the condition. Individuals with PMC should make time to rest and not push themselves too far. Also, they should limit physically exerting activities such as lifting heavy objects, as these might lead to muscle stiffness and a delay in the relaxation of contracted muscles.

Exercise 

While prolonged exercise is known to trigger myotonia, individuals with PMC can benefit from mild exercise, especially to keep the body warm and alleviate symptoms. However, rigorous exercises should be avoided.¹⁰

Massage

A gentle massage can improve blood circulation to muscles and provide a level of comfort for individuals with muscle stiffness. It can also help to manage pain caused by muscle cramps; however, it should be noted that while messaging can be soothing, it doesn’t make the symptoms go away. This is because massage does not cause the sodium channel to repolarise. 

Diet

Individuals with PMC should take good that is easy to chew and swallow as Individuals with PMC should eat foods that are easy to chew and swallow, this is because chewing hard foods can be rigorous, and some patients have reported an inability to continue chewing while others reported using their hands to close their jaws when they experience myotonia in the jaw as a result of chewing. Therefore, eating foods that are not crunchy and meats that are properly cooked and soft can help reduce symptoms of PMC.

Summary

PMC is a hereditary condition that results from the mutation of the gene that codes for the sodium channels in skeletal muscle. The result of this is the delayed ability of the muscle to relax after contraction, leading to muscle stiffness. It usually affects muscles in the face, throat, eyes, tongue, hands and legs. While PMC has symptoms that overlap with other myotonias, accompanying paralysis is one of its distinguishing features. Individuals with PMC can experience paralysis in their extremities and muscle cramping, which is usually accompanied by pain. The major conditions that trigger symptoms include: cold environments, cold drinks including ice cream, which can cause tongue myotonia, cold foods, stress, prolonged exercise, hard foods and prolonged exercise. While medications such as Mexiletine and Carbamazepine have been proven effective in relaxing muscles, acetazolamide is currently being used in managing the severity of muscle paralysis. However, certain non-drug approaches can alleviate symptoms, including reducing cold exposure, stress reduction, mild exercise, easy-to-chew and swallow foods, and massage. By adopting these approaches, parents can help their young ones manage symptoms and live better lives.

Frequently asked questions

What is myotonia?

Myotonia is a condition characterised by a delay in the muscles to relax after contraction, leading to muscle stiffness. 

What is a missense mutation?

A missense mutation is a type of point mutation where a single change in the DNA sequence leads to the substitution of one amino acid for another in the protein that is produced.

What is the polarisation of the sodium channel? 

This is the stage after contraction(or action potential) when the cell membrane potential is restored to its resting phase, leading to muscle relaxation.