Life With MND
What is PMA?
Progressive Muscular Atrophy (PMA) is a disorder of the lower motor neurones (LMNs). In comparison, the usual form of Motor Neurone Disease has both upper and lower motor neurone involvement. Lower motor neurones are a group of nerve cells in the spinal cord or in the brain that control muscles in the body. The lower motor neurone is at the bottom of the chain of command but if damaged the nervous system cannot control muscle movement and the muscles atrophy (die).
In Progressive Muscular Atrophy there is gradual loss of the lower motor neurones, so the muscles become steadily weaker and smaller, causing problems to the area of the body they serve. This results in progressive muscle weakness, fasciculations (rippling effect under the skin), and shrinkage in muscle bulk and weight loss.
In Progressive Muscular Atrophy there is gradual loss of the lower motor neurones, so the muscles become steadily weaker and smaller, causing problems to the area of the body they serve. This results in progressive muscle weakness, fasciculations (rippling effect under the skin), and shrinkage in muscle bulk and weight loss.
Facts about PMA
- PMA affects 5-7% of all people living with MND.
- Men are affected more than women and figures of 5:1 have been quoted, although this might be affected by the inclusion of undiagnosed Kennedy’s disease in the male group. Kennedy’s Disease is a rare form of Spinal Muscular Atrophy. Further information can be found on Inf02 Kennedy's Disease (69 kb) .
- Average age of onset is under 50 years, which is younger than MND.
Life expectancy is generally longer than for MND, averaging five – ten years. - PMA is held to be a form of MND and especially in the first four years after diagnosis clinical evidence of upper motor involvement may become apparent in some people. In others, the signs may always remain lower motor neurone in origin.
- PMA, like MND occurs sporadically in the majority of affected individuals. Sporadic is the term used for cases of the disease where there is no family history.
- PMA occasionally presents in families with a history of familial MND. Familial (or inherited) is the term used when more than one member of the family has been diagnosed with the disease. Further information can be found on information sheet B, ‘Inherited Motor Neurone Disease’.
How is it diagnosed?
PMA, like other forms of motor neurone disease, can be difficult to diagnose. It has to be recognised that, although the majority of people with PMA actually have the ‘lower motor neurone’ form of MND, about one third may have other forms of lower motor neurone disorders.
It is vitally important for your doctor or neurologist to review the diagnosis from time to time and this is why the initial investigations are so important. This helps to identify other forms of lower motor neurone disorders (Kennedy’s disease and other forms of spinal muscular atrophy; multifocal motor neuropathy etc).
Diagnosis is clinical and usually based on observation but does include an abnormal EMG. Diagnosis involves exclusion of all other possibilities, such as multiple sclerosis, spinal cord injury or tumours and motor neuropathies of other causes.
It is vitally important for your doctor or neurologist to review the diagnosis from time to time and this is why the initial investigations are so important. This helps to identify other forms of lower motor neurone disorders (Kennedy’s disease and other forms of spinal muscular atrophy; multifocal motor neuropathy etc).
Diagnosis is clinical and usually based on observation but does include an abnormal EMG. Diagnosis involves exclusion of all other possibilities, such as multiple sclerosis, spinal cord injury or tumours and motor neuropathies of other causes.
What are the tests?
Tests performed include:
- MRI scans to exclude abnormalities in brain or spinal cord
- Nerve conduction studies (small electric shocks to check speed of nerve conduction to the muscles)
- Electromyography (EMG): small needles placed in individual muscles to check for any dysfunction (abnormal in Lower Motor Neurone disease)
- Blood tests to check for other possible diseases
Electrophysiological tests (nerve stimulation) to the brain may also be carried out in an attempt to identify any upper motor neurone component which may not be evident on clinical examination.
An EMG test is a good way of detecting lower motor neurone disease, but has to be put into context with all of the other tests carried out, to eliminate all other possible diseases.
What are the symptoms?
PMA is characterised by:
- Muscle weakness
- Muscle atrophy
- Fatigue
- Fasciculations
- Cramps
- Muscle twitching
- Loss of reflexes
PMA starts most frequently with weakness in one hand, although it can be in one foot or the tongue. The weakness spreads to other muscles as the disease progresses; the affected muscles get smaller (atrophy) and fail to work. Cramps have usually preceded the first weakness and muscle twitching also occurs at an early stage. Both cramp and muscle twitching occur in normal health and therefore by themselves do not indicate any cause for concern.
Not having upper motor neurone involvement means that people living with PMA do not have the stiffness (spasticity) in their muscles, nor the very brisk reflexes and the uncontrollable emotions which MND often presents.
How might I be affected?
The first effects noticed will depend on where the disease starts. If the initial presentation is in the legs, then stumbling or difficulty climbing stairs may be noticed. If the initial weakness occurs in the arms, then loss of dexterity or an increase in dropping things may be the first signs. Cramps, twitching in muscles, aching muscles and general fatigue, can precede obvious weakness.
For a tiny percentage, PMA doesn’t spread from the initial area affected and although disabled, these people have a relatively benign course to their disease. An example could be bi-brachial amyotrophy (flail arm syndrome) which affects the arms, but often nowhere else. Even with this rare from of MND the rate of progression can be very variable.
For the majority, PMA continues to spread causing increasing disability and speech and swallowing can also become difficult. As breathing muscles are controlled by lower motor neurones, they can also be affected.
The final pathway for PMA is much the same as for MND, but without the upper motor neurone involvement and usually at a slower rate. However, as with all MND, PMA follows a different time course in each person and although average progression can be gauged for each individual affected it can be a very different experience.
For a tiny percentage, PMA doesn’t spread from the initial area affected and although disabled, these people have a relatively benign course to their disease. An example could be bi-brachial amyotrophy (flail arm syndrome) which affects the arms, but often nowhere else. Even with this rare from of MND the rate of progression can be very variable.
For the majority, PMA continues to spread causing increasing disability and speech and swallowing can also become difficult. As breathing muscles are controlled by lower motor neurones, they can also be affected.
The final pathway for PMA is much the same as for MND, but without the upper motor neurone involvement and usually at a slower rate. However, as with all MND, PMA follows a different time course in each person and although average progression can be gauged for each individual affected it can be a very different experience.
Management of PMA
As with MND, management of the disease is via support of the individual’s disabilities.
Assistive equipment may be needed for leg and arm weakness. Communication aids may be required. Feeding may become difficult and require assistance, e.g. via a PEG tube. Breathing may require support via NIPPV.
Further information can be found on Inf11 PEG Feeding (78 kb) , Inf14A Understanding how MND might affect your breathing (122 kb) and Inf14B Ventilation in MND (87 kb)
In all areas of support for the disease, professional assessment is advised, so that care is tailored to the individual.
