Progressive muscular atrophy (PMA): a rare form of motor neurone disease

Motor neurone disease affects the motor neurones, the nerve cells in the brain and spinal cord that tell muscles what to do. The NHS names 4 main types of MND: amyotrophic lateral sclerosis (ALS), which is the most common, progressive bulbar palsy, primary lateral sclerosis and progressive muscular atrophy.

The MND Association describes PMA as a rare form of MND that affects lower motor neurones. Muscles gradually lose mass, which is called atrophy or wasting, and become weak. People may also notice a twitching sensation that ripples under the skin, known as fasciculation.

PMA usually starts in the arms or legs and may only affect one part of the body for a number of years before spreading to other areas. Like other forms of MND, it typically affects people over 50, but younger people can be diagnosed, and it is slightly more common in men.

The early symptoms are very similar to other forms of MND, so PMA can be hard to identify at first. The NHS lists weakness in the hands as the early symptom of PMA, and the NHS general MND advice includes stiff or weak hands, weak legs and feet, and twitches or cramps. The MND Association lists the following as possible symptoms, noting that not everyone will experience all of them or in any particular order.

• Weakness and wasting of muscles in the legs, arms, hands and body.

• Muscle cramps and pain.

• Muscle twitching and rippling beneath the skin.

• Clumsiness.

• Breathing difficulties.

• Fatigue.

• Weight loss.

The NHS advises seeing a GP if you have difficulty holding or gripping objects, weakness in your legs or feet, or twitches or muscle cramps that keep happening, last a long time or do not go away. NHS inform similarly advises contacting the GP practice for early symptoms, because early referral to a specialist helps people access the right support. Early symptoms can be similar to less serious conditions, but they are worth checking.

For people already diagnosed, the MND Association advises contacting the health and social care team about breathing symptoms such as breathlessness at rest, shallow or rapid breathing, repeated chest infections, a weak cough, morning headaches or disturbed sleep. This is a good time to ask for referral to a local respiratory team.

A GP who suspects MND will usually refer to a neurologist. The NHS says tests may include blood tests, tests of how well the nerves work and an MRI scan to help rule out other conditions. NHS inform adds electromyography (EMG), nerve conduction tests and, less often, lumbar puncture or muscle biopsy, and explains that there is no single test for MND.

MND can be difficult to diagnose early. NHS inform notes that many first symptoms can be caused by more common conditions such as a trapped nerve or peripheral neuropathy, and that a period of observation may be needed, especially when the condition progresses slowly. MND can only be diagnosed when the symptoms are clearly getting worse.

The MND Association says it can take time to be sure that someone has PMA, and that the label can be reviewed and changed to another form of MND over time. If you are given a PMA diagnosis, it is reasonable to ask the neurologist how confident they are and what would prompt a review.

The MND Association says PMA usually progresses more slowly than most forms of MND and many people live for five years or more. The NHS says how long a person can expect to live depends on symptoms and the type of MND, and that the care team can discuss life expectancy for those who want to know. The experience varies from person to person, and not everyone wants to hear numbers.

It is helpful that PMA usually leaves time to plan. The MND Association notes that people with PMA have time to plan future needs, but it is worth thinking ahead in case there is a waiting list for equipment or services.

There is currently no cure for MND, but treatment can ease symptoms and help people have the best quality of life possible. The NHS says a team that may include a specialist nurse, a neurologist, a physiotherapist and an occupational therapist provides support, with an appointment with the care team every 2 or 3 months to review changes.

The NHS says riluzole may be offered to people with ALS to help slow progression, and NHS inform describes it as the only licensed medicine in the UK with a survival benefit in MND. Whether it is suitable for a given person is a decision for the specialist. Other medicines help specific symptoms, such as stiffness, cramps, drooling and breathlessness.

The MND Association gives practical advice for PMA. Exercise cannot reverse muscle weakness but may help flexibility and range of movement and maintain unaffected muscles. Pacing can reduce fatigue. Physiotherapy and medication may relieve cramps, and medication may help with twitching. An occupational therapist can assess equipment needs before purchases are made. A speech and language therapist and dietitian can help with swallowing and weight loss, and a feeding tube is one option some people choose. Breathing support is available if the breathing muscles weaken.

The MND Association states that people must inform the DVLA and their insurer of the diagnosis. It may eventually affect driving, but driving is often still possible when disability is mild, and the GP, consultant or MND care co-ordinator can advise.

Up to half of people with MND experience some changes in how they think, although the MND Association says this is less likely with PMA. Concerns about thinking or behaviour should be raised with the care team.

MND care in the UK is delivered mainly through NHS neurology services, MND care centres and community teams, with charity support from the MND Association and MND Scotland. Private neurology opinions are available and can help with diagnosis or second opinions, but ongoing multidisciplinary care and equipment are generally coordinated through the NHS and social care. The MND Association recommends an independent occupational therapy assessment before buying equipment, because private purchases can be costly and may not suit the home.