Parkinson's disease: symptoms, causes and treatment

Parkinson's disease is a long-term, progressive condition of the brain. The NHS describes it as a condition in which parts of the brain become progressively damaged over many years. The damage is concentrated in a small area called the substantia nigra, where nerve cells normally make dopamine. Dopamine acts as a messenger between the parts of the brain and nervous system that help control and co-ordinate body movements, so as it falls, movement becomes slower and less automatic.

The loss of cells is gradual. The NHS notes that symptoms usually only begin once around half of the nerve cell activity in the substantia nigra has been lost, which helps explain why the first signs can seem to appear from nowhere even though the process has been under way for some time. The condition is not the same for everyone: the order in which symptoms develop and how severe they become varies from person to person.

The three main symptoms affect physical movement. The NHS lists tremor, usually starting in a hand or arm and more likely when the limb is relaxed; slowness of movement, which can produce a distinctive slow, shuffling walk with very small steps; and muscle stiffness, which can make facial expressions and moving around difficult and may cause painful cramps.

Many other symptoms can accompany these and some can come first. A person is unlikely to have all of them. The NHS includes a reduced sense of smell, sometimes years before other symptoms, along with balance problems that make falls more likely, nerve pain, bladder urgency or night-time peeing, constipation, light-headedness on standing, excessive sweating, swallowing difficulty, drooling and poor sleep.

• Psychological: depression and anxiety are common, and mild memory or planning problems can develop.

• Cognitive: in some people the condition progresses to dementia, with more severe memory problems, personality change and sometimes visual hallucinations.

• Autonomic: blood pressure drops on standing, bladder and bowel changes, and sexual difficulties.

• Sleep: insomnia and daytime sleepiness are listed by the NHS, and can be made worse by night-time symptoms.

The honest answer is that it is not fully understood. The NHS says it is not known why the nerve cells are lost, and that a combination of genetic changes and environmental factors is believed to play a part. Faulty genes can run in families, but the NHS describes inheritance in this way as rare. Pesticides, herbicides and pollution have been suggested as contributors, yet the evidence linking environmental exposure to the condition is described as inconclusive.

It also helps to separate the disease from other causes of the same symptoms. Parkinsonism is the umbrella term for tremor, rigidity and slowness. Parkinson's disease is the most common type, but the NHS lists rarer forms with identifiable causes, including drug-induced parkinsonism (for example after some antipsychotic medicines, which usually improves once the medicine is stopped), other progressive brain conditions such as progressive supranuclear palsy and multiple system atrophy, and small strokes affecting several parts of the brain.

Parkinson's UK says you cannot catch Parkinson's from someone. The NHS says Parkinson's disease can run in families as a result of faulty genes being passed to a child, but it is rare for the disease to be inherited this way. A number of genetic factors have been shown to increase risk, and most experts think a combination of genetic and environmental factors is responsible.

The NHS says no test can conclusively show that you have Parkinson's disease. A doctor bases the diagnosis on your symptoms, your medical history and a detailed physical examination, and a GP may ask you to do simple tasks such as moving or walking around. In the early stages, when symptoms are usually mild, a GP may find it hard to say whether the condition is definitely present.

If a GP suspects the condition you will be referred to a specialist, usually a neurologist or a geriatrician, who will ask you to perform physical exercises so they can assess movement. The NHS adds that special brain scans, such as a SPECT scan, may be carried out in some cases to try to rule out other causes of the symptoms. Medicines taken for other reasons are also worth reviewing, because some can cause parkinsonism.

The NHS states there is currently no cure, but treatments can relieve symptoms and maintain quality of life. Early on, symptoms may be mild enough that no treatment is needed beyond regular specialist reviews. A care plan should be agreed with your healthcare team and your family or carers and reviewed regularly.

Three main medicine types are used: levodopa, dopamine agonists and monoamine oxidase-B (MAO-B) inhibitors. Most people eventually need levodopa, which is converted to dopamine in the brain and is usually combined with carbidopa or benserazide. Its benefit can become less long-lasting over the years and long-term use is linked with involuntary jerky movements (dyskinesias) and "on-off" effects. Dopamine agonists can cause sleepiness and, in some people, compulsive behaviours such as gambling or shopping, which carers are encouraged to watch for.

When tablets are not enough, the NHS lists apomorphine given by injection or pump, and medicines pumped continuously into the tummy through a tube for severe on-off fluctuations or involuntary movements. Deep brain stimulation, which uses an implanted pulse generator and fine wires placed in the brain, is available at specialist neuroscience centres but is not suitable for everyone. Supportive therapies matter as much as medicines: physiotherapy for stiffness and walking, occupational therapy for home safety and daily tasks, speech and language therapy for voice and swallowing, and dietitian advice for constipation, blood pressure and weight.

The NHS says that for some people with Parkinson's disease, dietary changes can help improve some symptoms. You may see a dietitian if your care team thinks you may benefit. Ask your care team before making major changes.

• To reduce constipation: increase the fibre in your diet and make sure you drink enough fluid.

• To avoid low blood pressure, such as dizziness when you stand up quickly: increase the amount of salt in your diet and eat small, frequent meals (the NHS gives this advice for some people; check with your team first).

• To avoid unintentional weight loss: ask for dietary changes tailored to you.

The NHS says symptoms get worse over time, so everyday activities can become harder without help. Many people respond well to treatment and have only mild to moderate disability, while a minority respond less well. The condition does not directly cause death, but the NHS notes it can make some people more vulnerable to serious infections, and that with modern treatment most people have a normal or near-normal life expectancy.

Practical help sits outside the hospital as well as in it. A local authority care and support needs assessment is available, and Parkinson's UK runs a free helpline and local support groups. Anyone considering complementary therapies is advised by the NHS to check with their care team first, because there is no clinical evidence they control symptoms and some herbal products, such as St John's wort, can interact unpredictably with Parkinson's medicines.

Most care is delivered through the NHS: a GP referral to a neurologist or a specialist in older people's medicine, followed by therapy teams and community support through the local authority. Deep brain stimulation and the infusion therapies are provided through specialist centres. Private neurology consultations exist and some people use them for a second opinion or faster first assessment, but long-term medicines, monitoring and therapy generally continue within NHS pathways, so it is worth asking how any private care would link back to your GP.