Getting diagnosed with a muscle wasting condition

There are many different types of muscle wasting and weakening conditions, and symptoms can vary significantly by condition and by person. You may find yourself at your GP if you have noticed that your child falls over more than their peers, you can no longer walk very far without feeling fatigued or if there is a family history of a condition. If you or a family member are experiencing symptoms which you’re concerned about, or which may be related to having a muscle wasting and weaking condition, contact your GP. Symptoms can vary significantly, however may include issues with your balance, falls, muscle weakness and wasting, movement or breathing difficulties, muscle fatigue or general tiredness from simple exercise.

Your GP may carry out some initial tests to try and find an explanation for your symptoms. However, since these conditions are often difficult to diagnose, you will usually be referred to a specialist for further investigation and diagnosis. This could be a genetics specialist or a neurologist with a specialist interest in muscle wasting and weakening conditions. They will use different methods to reach a clinical diagnosis that best explains your symptoms. As well as carrying out different tests, they may also discuss your family history. It’s important to note that diagnosis can be a lengthy process and can take some time. We understand this may difficult and we’re here to support you.

There are several tests that can be carried out to reach a diagnosis of a muscle wasting and weakening condition.

Blood tests

People with a suspected neuromuscular condition usually have their blood tested to check their creatine kinase (CK) levels. This is also called the CPK test. They may also have a blood test for genetic testing which can help to identify the cause of their symptoms.

CK is a protein – more specifically, an enzyme – that is normally found in muscle but can leak into the blood following muscle damage. The test measures the level of CK in the blood and clinicians can use this as a measure of muscle damage.

Although raised levels of CK in the blood point towards muscle damage, the test is not specific for damage caused by muscle wasting and weakening conditions. For example, a particularly hard session in the gym can also lead to increased CK levels. This means that the test result alone cannot conclusively provide an accurate diagnosis.

Magnetic Resonance Imaging (MRI)

MRI is a fast and non-invasive technique that can produce images of the inside of our bodies. Unlike an X-ray, which only shows our bones, MRI images can show the structure of different types of tissue such as muscle, fat, and bone.

Figure 1: Example of an MRI image of muscle

In the image above, you can see the muscles of the pelvis at the top, the thighs in the middle and lower legs at the bottom. The images on the left show a person who does not have a muscle wasting and weakening condition and the images on the right show someone with an RYR1-associated myopathy.

Muscle appears as a dark grey colour and fat appears as white. Most of the muscle in the person with the RYR1-associated myopathy has been replaced by fat.

An MRI scan can highlight which muscles are affected by a condition and can help to identify the most suitable muscle on which to perform a biopsy.

Muscle biopsy

A muscle biopsy is when a small piece of muscle is removed through a small cut or with a hollow needle. This will usually be from the leg or arm. The tissue sample enables clinicians to examine the muscle structure in detail, under a microscope.

Using dyes to stain specific proteins, clinicians can also identify proteins that are missing from the muscle. In some cases, this may provide a diagnosis.

However, in other conditions, where several genes may play a role in the biological pathway that produces the protein, further genetic testing may be required to identify the precise cause of the condition.

The clinician may also use other tests like electromyography (EMG) or nerve function tests both of which examine electrical activity in nerves and muscles.

By comparing when someone is at rest and when the muscles are contracting, clinicians can pinpoint the location of underlying problems – either in the muscles themselves, or in the nerves carrying signals to the muscles.

The results of clinical tests can help clinicians reach a diagnosis, however genetic testing can often provide a more precise diagnosis. Having a precise diagnosis can mean better access to treatment and better management of your condition.

Genetic tests are usually performed on a blood sample. They aim to identify which faulty gene is causing a condition and the precise nature of the genetic fault, in other words, the mutation.

There are several different types of mutation, which are named for their effect on the DNA.

For instance, a ‘deletion mutation’ is caused when some of the DNA is deleted and ‘duplications’ occur when part of the DNA is repeated. The clinical diagnosis suggests which gene (or genes) should be tested but often it does not point towards a single gene.

For example, the early symptoms of some cases of limb girdle muscular dystrophy can be hard to distinguish from other conditions, like Becker muscular dystrophy.

Some muscle wasting and weakening conditions can be caused by mutations in any one of several genes. In these cases, the gene that is most likely to cause the condition and symptoms is tested first.

If no mutation is found, the next most likely gene will be tested, and so on. In this case a diagnosis can take some time, depending on how many genes need to be tested.

If a genetic test is not available through the diagnostic service, samples are sent to laboratories where the DNA is analysed as part of ongoing research.

Sometimes a clinical diagnosis points clearly in the direction of a single gene, such as in Duchenne muscular dystrophy which points to the dystrophin gene. Tests will then focus on identifying the mutation in that gene.

In these cases, testing will look for the most common mutations (for example, deletions in Duchenne muscular dystrophy) and then gradually work towards rarer mutations.

Despite recent advances in identifying mutations that can cause muscle wasting and weakening conditions, clinicians will sometimes test all the known genes and still fail to identify the mutation causing the condition.

A precise genetic diagnosis allows clinicians to give their patients better information about how the condition will progress during their lifetime. It also allows the person to have better access to treatment and support for management of their condition. A precise genetic diagnosis can help individuals and families make preparations and informed family planning decisions. Some clinical trials require prospective participants to have a genetic diagnosis.

This may be because the therapy being tested targets the underlying genetic cause of the condition. For example, exon skipping therapies for Duchenne muscular dystrophy are mutation specific. This means that when these therapies are made available, they will potentially benefit only people with certain mutations.