Parkinson's Disease PDF

Parkinson Disease: 1-Parkinson disease (PD) is a chronic, progressive movement disorder resulting from loss of dopamine from the nigrostriatal tracts in the brain, and is characterized by rigidity, bradykinesia, postural disturbances, and tremor. 2-The age at onset of PD is variable, usually between...

Parkinson Disease: 1-Parkinson disease (PD) is a chronic, progressive movement disorder resulting from loss of dopamine from the nigrostriatal tracts in the brain, and is characterized by rigidity, bradykinesia, postural disturbances, and tremor. 2-The age at onset of PD is variable, usually between 50 and 80 years, with a mean onset of 55 years. 3-The symptoms of PD are progressive, and within 10 to 20 years, significant immobility results for most patients. Etiology: The etiology of PD is poorly understood. Most evidence suggests it is multifactorial, and attributable to a complex interplay between age-related changes in brain, underlying genetic risks, and environmental triggers. Pathophysiology: 1-Parkinson's disease is a degenerative process involving the dopaminergic neurons in the substantia nigra (the area of the basal ganglia that produces and stores the neurotransmitter dopamine). This area plays an important role in the extrapyramidal system, which controls posture and coordination of voluntary motor movements. 2-The loss of dopamine-producing neurons in the substantia nigra results in an imbalance between dopamine, an inhibitory neurotransmitter, and the excitatory neurotransmitter acetylcholine. This leads to an excess of excitatory acetylcholine at the synapse, and consequent rigidity, tremors, and bradykinesia. 3-Other nondopaminergic neurons may be affected, possibly contributing to depression and the other non-motor symptoms associated with this disease. Clinical Presentation of Parkinson’s disease: 1 PD develops insidiously and progresses slowly. Patients with PD display both motor and non-motor symptoms. The non-motor symptoms may precede the motor symptoms. Clinical features are summarized in Table 1(5) and figure 1. Table 1: Clinical Presentation of PD Motor Symptoms (TRAP) Non-motor Symptoms (SOAP) T = Tremor at rest (“pill S = Sleep disturbances (insomnia, restless legs syndrome(RLS)) *. rolling”) O = Other miscellaneous symptoms (problems with nausea, R = Rigidity (stiffness and fatigue, speech, pain, dysesthesias, vision, seborrhea) cogwheel rigidity) A = Autonomic symptoms (drooling, constipation, sexual A = Akinesia or dysfunction, urinary problems, sweating, orthostatic hypotension, bradykinesia dysphagia) P = Postural instability and P = Psychological symptoms (anxiety, psychosis, cognitive gait abnormalities impairment, depression) Restless legs syndrome (RLS), is characterized by one or more of the following: urge to move the legs, Relief of symptoms with movement , Onset or exacerbation of symptoms at rest , Onset or worsening of symptoms during nighttime (1). Video 1-Tremor motion in the hands is often described as “pill rolling,” since the fingers and thumbs move in opposition as though a small object was being rolled between them. 2-Bradykinesia is a slowing of movement. Slowness of movement characterized by a slow, shuffling gait and lack of arm swing. Movement becomes increasingly 2 impaired and can make turning in bed, rising from a low chair, and even walking increasingly difficult. 3-Postural instability is the primary cause of falls associated with PD. Signs include flexion at the knees, hips, and waist and walking on the balls of the feet. 4-Rigidity is an increase of muscle tone that is elicited when the examiner moves the patient's limbs, neck, or trunk (8). Rigidity of the face and trunk is often observable as a lack of facial expression (masked facies). The masking of facial expression may be misinterpreted as apathy, or depression. Treatment The goals of treatment are to minimize symptoms, disability, and side effects - while maintaining quality of life. A-Nonpharmacologic Therapy 1-Exercise, physiotherapy, and good nutritional support can be beneficial at the earlier stages to improve mobility, and enhance well-being and mood. 2-Speech therapy may be helpful, and psychological support is often necessary in dealing with depression and other related problems. B-Surgery 1-Deep brain stimulation (DBS) involves the implantation of a high-frequency device that provides electrical stimulation of the specific areas in the brain. 2- DBS is now the preferred surgical method for treating advanced PD that cannot be adequately controlled with medications. Pharmacotherapy: The primary objective of drug therapy is to enhance dopaminergic activity within the damaged areas of the basal ganglia, and this is achieved in various ways (Table 6.26). 3  1- L-Dopa and Carbidopa/L-Dopa L-dopa, the most effective drug available, is a precursor of dopamine. Unlike dopamine, carbidopa, L-dopa crosses the blood-brain barrier. Ultimately, all PD patients will require L-dopa. In the central nervous system (CNS) and peripherally, L-dopa is converted by l- amino acid decarboxylase (l-AAD) to dopamine. In the periphery, carbidopa can block l-AAD, thus increasing CNS penetration of administered L-dopa and decreasing dopamine adverse effects (eg, nausea, cardiac arrhythmias, postural hypotension, and vivid dreams). The usual maximal dose of L-dopa tolerated is approximately 1000 to 1500 mg/day. About 75 mg of carbidopa is required to effectively block peripheral l- AAD, but some patients need more. Carbidopa/L-dopa 25/100 mg tablet three times daily is the usual initial maintenance dose. 4  1- L-Dopa and Carbidopa/L-Dopa L-dopa, the most effective drug available, is a precursor of dopamine. Unlike dopamine, carbidopa, L-dopa crosses the blood-brain barrier. Ultimately, all PD patients will require L-dopa. In the central nervous system (CNS) and peripherally, L-dopa is converted by l- amino acid decarboxylase (l-AAD) to dopamine. In the periphery, carbidopa can block l-AAD, thus increasing CNS penetration of administered L-dopa and decreasing dopamine adverse effects (eg, nausea, cardiac arrhythmias, postural hypotension, and vivid dreams). The usual maximal dose of L-dopa tolerated is approximately 1000 to 1500 mg/day. About 75 mg of carbidopa is required to effectively block peripheral l- AAD, but some patients need more. Carbidopa/L-dopa 25/100 mg tablet three times daily is the usual initial maintenance dose. 4 After oral L-dopa administration, time to peak plasma concentrations varies intra- and intersubject. Meals delay gastric emptying, but antacids promote gastric emptying. L-dopa is absorbed primarily in the proximal duodenum via a saturable large neutral amino acid transport system, thus high-protein meals can interfere with bioavailability. Pharmacokinetic considerations (a) High-protein diets decrease absorption. (b) Immediate-release half-life 60–90 minutes, L-dopa is not bound to plasma proteins, and the elimination half-life is approximately 1 hour. Adding carbidopa can extend the half-life to 1.5 hours, and adding a COMT inhibitor (eg, entacapone) can extend it to approximately 2 to 2.5 hours. (c) Orally disintegrating tablet available; not absorbed sublingually (d) Slow-release considerations: Fewer daily doses; less plasma fluctuations; delay to effect; cannot crush; can divide. No measurable effect on “freezing” Note: The vitamin pyridoxine (B6) increases the peripheral breakdown of levodopa and diminishes its effectiveness. Long-term, L-dopa-associated motor complications can be disabling: 1-Wearing off effect The terms "off" and "on" refer to periods of poor movement (i.e., return of tremor, rigidity, or slowness) and good movement, respectively. Wearing off occurs when patients experience recurrence of symptoms before the next dose of medication. Possible options to solve such problem include: A-Carbidopa/L-dopa needs to be given more frequently so as to minimize daytime off episodes and to maximize on time. B- The addition of the COMT inhibitor entacapone or the MAO-B inhibitor rasagiline extends the action of L-dopa, and either should be considered. 5 C- A dopamine agonist (e.g., pramipexole, ropinirole) also can be added to a carbidopa/L-dopa regimen in an attempt to minimize the occurrence of wearing off. For acute off episodes, a subcutaneously administered short-acting dopamine agonist, apomorphine, is available and possesses a rapid onset of effect (within 20 minutes). It is administered as needed. Another complication of L-dopa therapy is dyskinesia 2-Dyskinesias.: Dyskinesia is an involuntary choreiform movements (too much movement) involving the neck, trunk, and lower/upper extremities. Dyskinesia usually is associated with peak dopamine levels (peak-dose dyskinesia). Such motor complications can occur 5–6 months after starting levodopa, especially when excessive doses are used initially Possible options to solve such problem include: A-The use of lower individual doses of L-dopa (with an increase in dosage frequency or addition of another agent to counteract the effects of using a lower L- dopa dose). B-Addition of amantadine that has antidyskinetic. 2- Dopamine Agonists 1- The ergot derivative bromocriptine and the nonergots pramipexole , rotigotine , and ropinirole are beneficial adjuncts in patients with limited clinical response to L-dopa. They decrease the frequency of “off” periods and provide an L-dopa- sparing effect. 2-The nonergots are safer and are effective as monotherapy in mild-moderate PD as well as adjuncts to L-dopa. 6 3-Note: important: Guidelines from the American Academy of Neurology support either dopamine agonists or levodopa as initial therapy for PD. A-In younger patients (e.g., age 65 years) with PD, it may be more appropriate to initiate treatment with levodopa instead of a dopamine agonist. The reason for this recommendations are: 1-There is less risk of developing motor complications from dopamine agonists than from L-dopa. Because younger patients are more likely to develop motor fluctuations, dopamine agonists are preferred in this population. 2-Older patients are more likely to experience psychosis from dopamine agonists; therefore, carbidopa/L-dopa may be the best initial medication in elderly patients. 3- Catechol-O-Methyltransferase (COMT) Inhibitors 1-Tolcapone and entacapone are used only in conjunction with carbidopa/L-dopa to prevent the peripheral conversion of L-dopa to dopamine. Thus, “on” time is increased by about ~1 to 2 hours. These agents significantly decrease “off ” time and decrease L-dopa requirements. 2- Tolcapone can cause hepatotoxicity. There is no evidence of hepatotoxicity from entacapone. But entacapone has short half life and must be give with each dose of L- dopa/carbidopa up to 8 times/day. 4- Monoamine Oxidase Type-B (MAO-B) Inhibitors 1-Inhibition of MAO-B is associated with reduced synaptic degradation of dopamine and prolonged dopaminergic activity. Two selective MAOB inhibitors, rasagiline and selegiline, are available for management of PD. 2-Selegiline is a first-generation MAO-B inhibitor that blocks dopamine breakdown and can modestly extend the duration of action of L-dopa (up to 1 7 hour). Selegiline is metabolized to the amphetamine derivatives , which have been implicated in producing side effects such as insomnia and vivid dreaming. A-It is not given in the evening because excess stimulation from metabolites can cause insomnia. B-The orally disintegrating tablet: formulation dissolves in the mouth on contact with saliva and undergoes pregastric absorption. This is an improvement over conventional selegiline because it minimizes the effect of first-pass metabolism and results in higher plasma concentrations of selegiline and reductions in the amphetamine-based metabolites. 3-Rasagiline is a second-generation selective inhibitor of MAO-B. It is indicated as monotherapy in early disease or as adjunct therapy to levodopa in advanced disease. A-Rasagiline is differentiated from selegiline primarily in that it is a more potent inhibitor of MAO-B, and it is not metabolized into amphetamine-based metabolites. B-When an adjunctive agent is required for managing motor fluctuations, rasagiline may provide 1 hour of extra “on” time during the day. It is considered a first-line agent (as is entacapone) for managing motor fluctuations. 5- Anticholinergic Medications 1-Anticholinergics (e.g. procyclidine, and trihexyphenidyl (benzhexol)) are more helpful in alleviating tremor and rigidity than bradykinesia (rarely show substantial benefit for bradykinesia). However, they are poorly tolerated by elderly patients owing to their cognitive side effects. 2-Their use is mostly restricted to patients with tremor that is intractable to levodopa treatment. 8  6- Amantadine 1-For patients with mild signs and symptoms, amantadine monotherapy may be considered. Amantadine reduces all the symptoms of parkinsonian, usually within days after starting therapy; however, long-term use is limited in many patients by the development of tachyphylaxis within 1 to 3 months. 2-Aamantadine has been found to have antidyskinesia effects, the finding has shifted its emphasis from use as monotherapy in early disease to that of an adjunctive agent in managing levodopa-induced dyskinesias. (Because excess glutamatergic activity has been implicated in the pathophysiology of dopaminergic dyskinesias and amantadine has glutamate-antagonist properties). General approach to treat Parkinson disease. 1-Monotherapy usually begins with a monoamine oxidase-B (MAO-B) inhibitor, or if the patient is physiologically young, a dopamine agonist. 2-For patients who are older, cognitively impaired, or having moderately severe functional impairment, L-dopa (e.g., carbidopa/levodopa) is preferred. 3- With the development of motor fluctuations: A- addition of a COMT inhibitor should be considered to extend L-dopa duration of activity. B-Alternatively, addition of a MAO-B inhibitor or dopamine agonist should be considered. C- For management of L-dopa-induced peak-dose dyskinesias, the addition of amantadine should be considered. 9 Surgery: 1-Deep brain stimulation involves the implantation of a high-frequency device that provides electrical stimulation of the specific areas in the brain. 2-Deep brain stimulation is reserved for patients who have a good response to levodopa but in whom dyskinesias or response fluctuations are problematic. 10  Deep brain stimulation. A pulse generator, sends high frequency electrical impulses to the thalamus, thereby blocking the nerve pathways associated with tremors in Parkinson disease. Prognosis 1-The outlook for patients with Parkinson's disease is variable, and depends partly on the age of onset. 2-If symptoms start in middle life, the disease is usually slowly progressive and likely to shorten lifespan because of the complications of immobility and tendency to fall. 3-Onset after 70 is unlikely to shorten life or become severe. Management of Common Nonmotor Symptoms of Parkinson’s Disease: Pharmacologic and nonpharmacologic treatment interventions for nonmotor symptoms of Parkinson’s disease are summarized by the following tables (table 2, 3 and 4). 11 12