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Learn about NDM

What is NDM?

Non-dystrophic myotonia, or NDM, refers to a group of diseases that affect muscles. The number of people with NDM varies in different countries, but on average approximately 1 in every 100,000 people worldwide are affected by NDM, and it is therefore classed as a rare disease.1

There are several forms of NDM, however all types share a common symptom called myotonia. Myotonia means that one’s muscles are not able to relax immediately after they have been used.2 Myotonia may be experienced as stiffness, cramps or locking of your muscles during everyday tasks and activities. People with NDM may also experience pain and fatigue.3 Most people with NDM start to notice symptoms in childhood or early adulthood, however it may be some time before they are diagnosed.3

“Sometimes my muscles remain tense and stiff but, at the same time, they lose all strength and then I lose control.”

— HJ, Paramyotonia congenita

What causes NDM?

NDM is caused by a mutation in a gene, which prevents muscles from relaxing normally.2 NDM is inherited, however the ways in which it is passed on depends on the type of NDM that you have.

Learn more about the causes and symptoms of NDM, and how it can be inherited.

Types of NDM

NDM is not a single condition, it is a group of disorders, which share similar symptoms. The four main types are commonly known as Becker myotonia congenita, Thomsen myotonia congenita, paramyotonia congenita (Eulenburg) or dyskalaemic periodic paralysis.1,4 If you or your doctor think you have NDM, it is important to work with your healthcare team to understand what type of NDM you have, so that you can manage your symptoms in the best way possible.

The figure below shows how people with different types of NDM typically experience their symptoms.

Can NDM be treated?

Most people with NDM can adapt the way they do things to manage their symptoms. If your symptoms are affecting your daily life, you may wish to seek further advice from a healthcare professional who specialises in rare conditions affecting the muscles, like NDM.

There is currently no cure for NDM, but you can learn more about managing the symptoms of NDM and how to find specialist healthcare advice.

References
  • Hahn C, Salajegheh MK. Iran J Neurol 2016;15:46–53
  • Matthews E et al. Brain 2010;133:9–22
  • Vereb N. J Neurol. 2021; 268(5): 1708–1720
  • Trivedi JR, et al. Brain 2013;136:2189–2200

UK-NDM-2202-00003 February 2022

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Foods to avoid on a low-potassium diet*

  • Fruit1,2
  • Vegetables1,2
  • Beans/legumes1,3
  • Other1-3
  • Avocado
  • Artichoke
  • Baked beans
  • Bran cereal
  • Apricots
  • Beetroot
  • Kidney beans
  • Dairy (eg yoghurt, milk)†
  • Bananas
  • Brussel sprouts
  • Lentils
  • Nuts
  • Dried fruits eg dates, raisins and prunes
  • Broccoli (cooked)
  • Brown rice
  • Grapefruit
  • Okra
  • Salt substitutes
  • Kiwi
  • Parsnip
  • Wholewheat bread and pasta
  • Mango
  • Potatoes (processed or with skin on)
  • Melons
  • Cooked spinach
  • Nectarines
  • Tomato (concentrated, eg. Tomato puree)
  • Oranges and orange juice
  • Papaya
  • Pomegranate and pomegranate juice

  • Fruit1,2

    Avocado

    Apricots

    Bananas

    Dried fruits eg dates, raisins and prunes

    Grapefruit

    Kiwi

    Mango

    Melons

    Nectarines

    Oranges and orange juice

    Papaya

    Pomegranate and pomegranate juice

  • Vegetables1,2

    Artichoke

    Beetroot

    Brussel sprouts

    Broccoli (cooked)

    Okra

    Parsnip

    Potatoes (processed or with skin on)

    Cooked spinach

    Tomato (concentrated, eg. Tomato puree)

  • Beans/legumes1,3

    Baked beans

    Kidney beans

    Lentils

  • Other1-3

    Bran cereal

    Dairy (eg yoghurt, milk)†

    Nuts

    Brown rice

    Salt substitutes

    Wholewheat bread and pasta

*Meat and fish contain a moderate amount of potassium but they are an important source of protein so shouldn’t be avoided; †Dairy products contain potassium but are an important source of calcium so should be consumed in moderation
References
  • WebMD. Low-potassium diet: what to know? Available at: https://www.webmd.com/food-recipes/low-potassium-diet-foods ; Accessed February 2022
  • St Georges Kidney Patients Association. Eating on a low potassium diet. Available at: https://www.sgkpa.org.uk/main/eating-well-on-a-low-potassium-diet-2 ; Accessed February 2022
  • NHS. Information for people on a low potassium diet. Available at: https://www.nth.nhs.uk/content/uploads/2019/02/PIL1061-Information-for-people-following-a-low-potassium-diet-Final-11.02.19-LP.pdf ; Accessed February 2022
  • NDM type1
  • Symptoms2,3
  • Which type of ion channel? 2,3
  • How is it inherited?2,3

  • Thomsen myotonia congenita

    (also called Thomsen myotonia or autosomal dominant myotonia congenita)
  • Lower limbs tend to be more affected, although can also affect the arms, hands and face. Stiffness may be worse when you first try to move after a period of inactivity, and may ease as you ‘warm up’.
  • Chloride (Cl-)
  • Autosomal dominant

  • Becker myotonia congenita

    (also called Becker myotonia, Becker disease, generalized myotonia, recessive generalized myotonia or autosomal recessive myotonia congenita
  • Lower limbs tend to be more affected, although can also affect the arms, hands and face. Stiffness may be worse when you first try to move after a period of inactivity, or if you are startled, and may ease as you ‘warm up’. Sometimes people with Becker myotonia congenita experience temporary weakness after an episode of myotonia.
  • Chloride (Cl-)
  • Autosomal recessive

  • Paramyotonia congenita

    (Also called Eulenburg disease, paralysis periodica paramyotonia, paramyotonia congenita of von Eulenburg, PMC or von Eulenburg’s disease)
  • Myotonia mainly affects hands and face and gets worse with exercise. Cold is also a key trigger of myotonia, and muscle weakness after an episode of myotonia may last hours or sometimes days.
  • Sodium (Na+)
  • Autosomal dominant

  • Sodium channel myotonia, SCM:

    myotonia permanens and myotonia fluctuans, acetazolamide-responsive myotonia (ARM) previously known as Potassium aggravated myotonias (PAM)
  • Potassium-aggravated myotonia is a rare form of NDM that affects all areas of the body. Myotonia attacks are triggered by eating potassium-rich foods. Symptoms may fluctuate widely from day to day (myotonia fluctuans) or are constant and severe (myotonia permanens).
  • Sodium (Na+)
  • Autosomal dominant

  • Other closely related sodium disorders with myotonia

    (including hyperkalemic paralysis or hyperPP)
  • Myotonia is usually mild, and often involves the eyelids, hands, and tongue. Attacks of weakness can occur at any time and are commonly triggered by rest following exercise, fasting, eating potassium-rich foods or stress.
  • Sodium (Na+)
  • Autosomal dominant
References
  • Stunnenberg B. Muscle Nerve. 2020 Oct; 62(4): 430–444
  • Hahn C, Salajegheh MK. Iran J Neurol 2016;15:46–53
  • Matthews E, et al. Brain 2010:133; 9–22

  • NDM type1

    Thomsen myotonia congenita

    (also called Thomsen myotonia or autosomal dominant myotonia congenita)

    Becker myotonia congenita

    (also called Becker myotonia, Becker disease, generalized myotonia, recessive generalized myotonia or autosomal recessive myotonia congenita

    Paramyotonia congenita

    (Also called Eulenburg disease, paralysis periodica paramyotonia, paramyotonia congenita of von Eulenburg, PMC or von Eulenburg’s disease)

    Sodium channel myotonia, SCM:

    myotonia permanens and myotonia fluctuans, acetazolamide-responsive myotonia (ARM) previously known as Potassium aggravated myotonias (PAM)

    Other closely related sodium disorders with myotonia

    (including hyperkalemic paralysis or hyperPP)

  • Symptoms2,3

    Lower limbs tend to be more affected, although can also affect the arms, hands and face. Stiffness may be worse when you first try to move after a period of inactivity, and may ease as you ‘warm up’.

    Lower limbs tend to be more affected, although can also affect the arms, hands and face. Stiffness may be worse when you first try to move after a period of inactivity, or if you are startled, and may ease as you ‘warm up’. Sometimes people with Becker myotonia congenita experience temporary weakness after an episode of myotonia.

    Myotonia mainly affects hands and face and gets worse with exercise. Cold is also a key trigger of myotonia, and muscle weakness after an episode of myotonia may last hours or sometimes days.

    Potassium-aggravated myotonia is a rare form of NDM that affects all areas of the body. Myotonia attacks are triggered by eating potassium-rich foods. Symptoms may fluctuate widely from day to day (myotonia fluctuans) or are constant and severe (myotonia permanens).

    Myotonia is usually mild, and often involves the eyelids, hands, and tongue. Attacks of weakness can occur at any time and are commonly triggered by rest following exercise, fasting, eating potassium-rich foods or stress.

  • Which type of ion channel? 2,3

    Chloride (Cl-)

    Chloride (Cl-)

    Sodium (Na+)

    Sodium (Na+)

    Sodium (Na+)

  • How is it inherited?2,3

    Autosomal dominant

    Autosomal recessive

    Autosomal dominant

    Autosomal dominant

    Autosomal dominant

References
  • Stunnenberg B. Muscle Nerve. 2020 Oct; 62(4): 430–444
  • Hahn C, Salajegheh MK. Iran J Neurol 2016;15:46–53
  • Matthews E, et al. Brain 2010:133; 9–22