Parkinson's syndrome

Parkinson's syndrome. Parkinson's syndrome, also known as parkinsonism, is a clinical syndrome characterized by a core set of motor signs resulting from dysfunction in the basal ganglia circuits of the brain. It encompasses a spectrum of disorders, with the most common being idiopathic Parkinson's disease, but also includes several other neurodegenerative and secondary conditions. The diagnosis is primarily clinical, based on the presence of cardinal motor features, and management focuses on symptomatic relief and improving quality of life.

Definition and classification

Parkinson's syndrome is defined by the presence of bradykinesia in combination with at least one of the following: muscle rigidity, resting tremor, or postural instability. It is broadly classified into primary (idiopathic) parkinsonism, secondary (acquired) parkinsonism, and parkinsonism-plus syndromes. The primary form is idiopathic Parkinson's disease, a distinct neurodegenerative disorder. Parkinsonism-plus syndromes include conditions like multiple system atrophy, progressive supranuclear palsy, and corticobasal degeneration, which feature additional neurological signs. Secondary causes encompass drug-induced parkinsonism, vascular parkinsonism from cerebrovascular disease, and parkinsonism due to toxin exposure or other identifiable insults.

Causes and pathophysiology

The pathophysiology involves dysfunction or degeneration of neurons in the substantia nigra pars compacta and their projections to the striatum, leading to a critical deficiency of the neurotransmitter dopamine. In idiopathic Parkinson's disease, this is associated with the accumulation of abnormal alpha-synuclein proteins into Lewy bodies. For other syndromes, different pathological proteins are implicated; for instance, tau protein aggregates are characteristic of progressive supranuclear palsy. Secondary causes include medications that block dopamine receptors, such as antipsychotics, strokes affecting the basal ganglia, and exposure to toxins like MPTP. Genetic factors play a role in some familial forms, involving genes like LRRK2, PARK7, and SNCA.

Signs and symptoms

The cardinal motor symptoms are bradykinesia, rigidity, resting tremor (often described as "pill-rolling"), and postural instability. Non-motor symptoms are prevalent and can precede motor signs by years, including anosmia, rapid eye movement sleep behavior disorder, constipation, and dysautonomia. Neuropsychiatric features such as depression, anxiety, apathy, and later dementia are common. Other associated problems include hypomimia (reduced facial expression), hypophonia (soft speech), micrographia, dysphagia, and gait freezing. Parkinsonism-plus syndromes present with additional features like early falls in progressive supranuclear palsy or cerebellar signs in multiple system atrophy.

Diagnosis

Diagnosis is clinical, based on history and neurological examination, often utilizing criteria like those from the Movement Disorder Society. Key is the positive response to a trial of levodopa, which is supportive of idiopathic Parkinson's disease. Neuroimaging can aid in differential diagnosis; a DaTscan (dopamine transporter scan) can demonstrate reduced dopamine transporter binding in the striatum, helping to distinguish from conditions like essential tremor. Magnetic resonance imaging may show patterns suggestive of vascular parkinsonism or atrophy in specific regions for progressive supranuclear palsy. Conditions like Wilson's disease should be ruled out in younger patients.

Management and treatment

The cornerstone of pharmacological treatment is dopamine replacement therapy, primarily with carbidopa/levodopa. Other medications include dopamine agonists like pramipexole and ropinirole, MAO-B inhibitors such as rasagiline and selegiline, and COMT inhibitors like entacapone. For refractory motor fluctuations and dyskinesias, device-aided therapies are considered, including deep brain stimulation targeting the subthalamic nucleus or globus pallidus internus, and levodopa-carbidopa intestinal gel infusion. Non-pharmacological management is vital and includes physical therapy, occupational therapy, and speech-language pathology. Treatment of non-motor symptoms, such as psychosis with pimavanserin, is also a critical component of care.

Prognosis and epidemiology

Parkinson's syndrome is a progressive disorder with variable prognosis depending on the underlying cause. Idiopathic Parkinson's disease typically has a more indolent course compared to parkinsonism-plus syndromes like multiple system atrophy, which progress more rapidly. Life expectancy may be reduced, with complications like pneumonia due to dysphagia being common causes of mortality. Epidemiologically, it increases in prevalence with age, affecting approximately 1% of the population over 60 years and 3% over 80 years. Incidence and prevalence rates vary globally, with studies showing differences across regions in North America, Europe, and Asia. Established risk factors include increasing age, male sex, and exposure to certain pesticides. Category:Neurological disorders Category:Movement disorders Category:Parkinson's disease