Parkinson's Disease: Diagnosis and Treatment
Diagnosis
Parkinson's disease is diagnosed clinically based on the presence of bradykinesia plus either rest tremor or rigidity, without requiring specialized testing in typical presentations. 1, 2
Core Diagnostic Features
- Bradykinesia (slowness of movement) must be present along with at least one of the following: rest tremor, rigidity, or loss of postural reflexes 1, 2
- Look for asymmetric onset of symptoms, which is characteristic of idiopathic Parkinson's disease 1
- Assess for secondary motor features including hypomimia (reduced facial expression), micrographia (small handwriting), shuffling gait, and festination 1
Prodromal Features to Identify
- REM sleep behavior disorder (acting out dreams) 2
- Hyposmia (reduced sense of smell) 2
- Constipation 2
- Depression and anxiety 2
When to Use Imaging
- Order DaTscan (Ioflupane SPECT/CT) when clinical presentation is uncertain to differentiate Parkinsonian syndromes from essential tremor or drug-induced tremor; a normal scan essentially excludes Parkinson's disease 3
- Obtain brain MRI without contrast to evaluate for atypical Parkinsonisms (Multiple System Atrophy, Progressive Supranuclear Palsy, Corticobasal Degeneration), though MRI is often normal in early idiopathic Parkinson's disease 3
Red Flags Suggesting Alternative Diagnosis
- Poor or absent response to levodopa 1
- Early occurrence of gait difficulty, postural instability, or dementia 1
- Early hallucinations or severe dysautonomia 1
- Presence of ophthalmoparesis, ataxia, or other atypical features 1
Pharmacologic Treatment
Levodopa/carbidopa is the most effective first-line treatment for motor symptoms and should be initiated in most patients with functional impairment. 4, 5, 3
Levodopa Administration Protocol
- Administer levodopa at least 30 minutes before meals to avoid competition with dietary proteins for absorption across the intestinal wall and blood-brain barrier 4, 5
- Start with carbidopa 50 mg combined with appropriate levodopa dosing 3
- For tube-fed patients, interrupt enteral nutrition for at least 1 hour before and 30-40 minutes after levodopa administration 5
Dietary Optimization
- Implement a protein redistribution diet (low-protein breakfast and lunch, normal protein intake only at dinner) to improve motor function and increase "ON" time in patients with motor fluctuations 4, 5
- Monitor for complications of protein redistribution including weight loss, micronutrient deficits, hunger before dinner, and worsening dyskinesias 5
- Avoid strict low-protein diets as they lack supporting evidence and may cause nutritional deficiencies 5
Nutritional Monitoring
- Regularly monitor vitamin B12 and folate levels, as levodopa may cause hyperhomocysteinemia, especially in older patients and those with long-standing disease 4, 5
- Supplement vitamin D, folic acid, and vitamin B12 when deficiencies are identified 5
- Monitor body weight regularly, as weight loss correlates with disease progression 5
- Screen for medication side effects affecting nutrition: nausea, vomiting, constipation, weight loss, dry mouth, anorexia, and changes in taste/smell 4, 5
Management of Motor Complications
Dyskinesias
- When dyskinesias emerge or worsen, reduce levodopa doses 4, 5
- If dyskinesias remain troublesome despite medication optimization, consider deep brain stimulation targeting the globus pallidus internus (GPi) 4
Deep Brain Stimulation (DBS)
Consider DBS for patients with motor complications (motor fluctuations, medication-resistant tremor, dyskinesias) despite optimal medical management. 4, 5, 2
Target Selection Algorithm:
- Choose subthalamic nucleus (STN) when the primary goal is reduction of dopaminergic medications 4
- Choose GPi when:
- Both STN and GPi provide equivalent improvements in motor scores and quality of life measures 4, 5
Non-Pharmacologic Treatment
Exercise and Rehabilitation
- Exercise and rehabilitative therapy (physical, occupational, and speech therapy) complement pharmacologic treatments and should be part of routine management 2
Constipation Management
- Recommend fermented milk containing probiotics and prebiotic fiber in addition to increased water and fiber intake 6, 4, 5
- This approach has demonstrated increased complete bowel movements, improved stool consistency, and reduced laxative use 6
Dysphagia Management
- Optimize antiparkinsonian treatment to ameliorate motor symptoms contributing to swallowing difficulties 5
Common Pitfalls and Caveats
- Do not administer levodopa with high-protein meals, as this significantly reduces drug absorption and efficacy 4
- Increasing doses of levodopa over time are associated with higher risk for malnutrition, requiring careful monitoring 5
- Axial signs (dysarthria, dysphagia, postural instability, freezing) and most nonmotor symptoms (depression, cognitive decline, dysautonomia) typically do not respond satisfactorily to levodopa and require alternative management strategies 7
- Gastrointestinal dysfunction (dysphagia, constipation, gastroparesis) can impair levodopa efficacy by reducing bioavailability 5