Parkinson’s disease (PD) is a neurodegenerative disorder characterized by the development of motor symptoms such as slowness, rigidity, resting tremor and impaired postural reflexes, and can be associated with balance and speech problems. Frequently, PD is also associated with a range of non-motor symptoms such as memory problems and progressive cognitive impairment, depression, loss of motivation, compulsive behaviors and hallucinations among others.
PD is caused by the progressive loss of certain populations of neurons, with those involved in the production of a neurotransmitter called dopamine being particularly vulnerable. At the same time, in the nervous system of patients with PD there are aggregates of certain types of proteins related to neuronal damage known as Lewy bodies. PD affects up to 1% of the population over 60 years of age and represents the second most frequent neurodegenerative disease, after Alzheimer’s disease. Although it is a disease that typically affects people in adulthood, 10% of cases occur in people under 40 years of age in what we call the early-onset variant of PD.
It is important to note that, despite the generalized idea that all patients with PD present tremor, about half of the cases present without manifesting this symptom.
What causes Parkinson’s disease?
Most cases of PD are “idiopathic” in origin. This means that the cause is unknown. It is currently assumed that multiple triggering factors predispose to the development of the disease. Although the exact mechanisms that lead to the development of PD are not known, there are some genetic mutations that are associated with an increased risk of developing the disease, as well as certain mutations that are associated with familial, autosomal dominant forms of early-onset Parkinson’s disease.
What are the symptoms of Parkinson’s disease and its treatment?
The symptoms of PD can be divided into what we call motor symptoms and non-motor symptoms. Although some of these symptoms are more common in later stages of the disease, many of the symptoms associated with PD can appear at any time during the course of the disease.
People affected by PD usually present slowness, clumsiness, stiffness or tremor that usually starts on one side of the body and limb and progressively affects the whole body. In some cases, initially the patient or family members detect a certain tendency to drag one of the lower extremities when walking, to not swing the arms, to be more clumsy, slow or present a form of tremor when at rest, that is, while not performing any activity.
A neurological examination by a physician specializing in movement disorders can detect whether the symptoms presented by the patient are compatible with PD or have another cause.
Although PD was historically considered to be an exclusively motor disorder, today it is indisputable that there is a whole set of non-motor symptoms that are inseparable from the disease.
Among the most frequent are depressive symptoms, which in some cases may even precede the onset of motor symptoms, anxiety, loss of interest and motivation, sleep disorders, visual hallucinations or irritability, among others. Some of these symptoms occur as a consequence of a lack of dopamine, in other cases they may be due to an excess in the dose used. Therefore, the therapeutic adjustment of the drugs used can in many cases totally or partially resolve this symptomatology.
A side effect that develops in about 20% of patients using a type of drug called “dopaminergic agonists” is the so-called impulse control disorders. In these cases, patients develop obsessive and compulsive behaviors in a poorly controlled manner that incite them to perform actions with which they associate pleasure. Some of the impulse control disorders most frequently found in PD are pathological gambling or compulsive gambling, obsessive ideas about sex or compulsive eating, among others. Obviously, many of these behaviors have a very negative impact on the patient and his or her environment, and on many occasions neither the patients nor their relatives are aware that these behaviors are a side effect. When these problems are detected, the management of the doses and type of drugs used can in many cases restore normality.
At the cognitive level, PD patients have some type of difficulty with respect to their pre-diagnostic level of disease. These difficulties often include problems with attention span, organization and in some cases problems with memory and word finding. Unlike Alzheimer’s disease, having some cognitive problems does not mean that one will suffer from dementia in the future. However, a significant proportion of people with PD will experience a more or less aggressive cognitive decline during the first 5 years of disease progression, which in some cases may lead to PD-associated dementia.
Other non-motor symptoms frequently found in PD include sleep disturbances, constipation problems, fatigue, pain and changes in sexual appetite and behavior.
What are the most effective treatments?
Treatment of motor symptoms in PD is by dopaminergic replacement therapies, that is, by drugs that increase the levels of the neurotransmitter dopamine that the degenerative process has been decreasing. With optimal pharmacological management, many people in early stages of PD show an excellent response that can be maintained for several years without any functional limitation.
The progression of PD is associated with complications of motor symptoms and a worse response to the usual pharmacological treatments, and a thorough review is then necessary and it is even possible to consider what we call advanced treatments. This type of treatment includes the implantation of devices that automatically release certain amounts of drug continuously, thus limiting the motor fluctuations typical of the disease. Other options to consider include deep brain stimulation which consists of a neurosurgical procedure through which a system of electrodes is implanted in the patient’s nervous system as a “pacemaker” and manages to significantly restore brain function and consequently, movement control.
Although there are no curative treatments for cognitive disorders or dementia in PD, it is essential to assess the cognitive status of patients in order to identify possible indicators of cognitive impairment to help us implement strategies aimed at slowing its progression.
For non-motor symptoms, treatment may include adjustment of medication, initiation of other pharmacological treatments and the use of complementary therapies such as change of eating habits, care of sleep quality, psychotherapy or physical exercise, among others.