How can doctors decide if I have NDM?

Non-dystrophic myotonia, or NDM, refers to a group of rare diseases that affect muscles.1,2 Because NDM is rare, it may not be the first condition a doctor thinks of when you tell them about your symptoms. Often it takes people with NDM several years before they find out what is causing their problems.3

Your healthcare team may need to run several tests to be sure that they get your diagnosis correct. NDM cannot be diagnosed with one single test.2 Also, as NDM includes a number of conditions with similar symptoms, your doctor will want to make sure they know exactly what type of NDM you have so that they can help you manage your symptoms in the best way possible. If you are unsure about any aspect of any test, don’t be afraid to ask a member of your healthcare team for more information.

History of symptoms

A doctor may first suspect NDM after carefully listening to your history of symptoms.3 They will need to know when you first started to notice stiffness in your muscles, which muscles are affected and when symptoms are better or worse. Symptoms of NDM can change from day to day. Tracking your symptoms in a diary may help you unlock any patterns that can help your doctor identify which type of NDM you may have.

Clinical examination

Your doctor may wish to examine your muscles for signs of NDM.2 Although for many people with NDM their muscles may appear normal, in some cases affected muscles may be well defined or conversely, exhibit signs of weakness. Your doctor may ask you to repeatedly clench and unclench your fist, close and open your eyes, stand up and walk around a chair, or climb stairs to check for signs of myotonia.

Electromyography (EMG)

Myotonia can be checked for by using a test called an electromyography (also referred to as an EMG), which measures the electrical signalling in your muscles.2,4,5 During the procedure, a small needle carrying a fine wire will be inserted into your muscle to measure the activity. Some people may find this uncomfortable, but it will not harm you and any uncomfortable sensations will stop once the procedure has finished.

While you are having an electromyograph, your doctor may ask you to carry out a short or long exercise test; these can help them distinguish which kind of NDM you might have.2,4,5 They may also ask you to repeat the test after some rest or cooling the muscle being investigated.

Genetic analysis

NDM is caused by a mutation in the genes responsible for making sodium and chloride ion channel proteins in your muscle cells. Over 265 different mutations have been recorded in people with NDM,6 and it is possible to test for mutations in all the genes that may be involved in NDM at the same time, using one genetic test.2 Identifying what mutation you are carrying will help your doctor decide what type of NDM you have, and how best to manage your symptoms. To have a genetic analysis, you will need to have a blood sample taken.

References
  • Stunnenberg BC, et al. Muscle Nerve 2020;62:430-444
  • Matthews E, et al. Pract Neurol 2021;0:1-10
  • Matthews E. Brain 2010; 133(1):9–22
  • Fournier E. Ann Neurol 2004;56:650–61
  • Fournier E. Ann Neurol 2006;60:356–65
  • Morales F and Pusch M. Front Neurol 2020;10:1404

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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 March 2021
  • 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 March 2021
  • 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 March 2021
  • 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