Neurodegenerative Disorders/Parkinsons Flashcards
Define neurodegeneration
progressive loss of neuronal function, usually w/neuronal cell death and protein aggregates (inclusion bodies)
What are the 4 major neurodegenerative diseases?
Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, Amyotrophic lateral sclerosis (ALS)
Parkinson’s symptoms
resting tremor (“shaking palsy”), bradykinesia, akinesia, muscle rigidity, postural instability, dementia
What are the two most common causes of misdiagnosis for Parkinson’s?
1) Essential tremor (vs resting tremor in PD)
2) Shuffling gait (vs. gait/postural disorders in PD)
How to dx PD tremor? bradykinesia? ridigity? gait/posture?
1) tremor - handwriting differences (micrographia), slower tremor than essential
2) finger tapping test
3) cog wheel or ratchet “catch and release”
4) foot dragging, arm swing reduced on affect side, feet close together, stooped posture, difficulty turning
What are some causes of Parkinsonism
stroke, brain trauma, anesthesia, encephalitis, meningitis, antipsychotic drugs, anti-emetics, intoxication, CO poisoning, etc
Neurological basis for Parkinson’s
Major symptoms caused by depletion of dopamine NT in the substantia nigra pars compacta (80% loss of neurons).
Parkinson’s risk factors
genetics, age (CNS infections), environmental factors/toxins, oxidative stress, glutamate excitotoxicity, protein misfolding, mutations
Dopamine biosynthesis pathway
1) tyrosine–>L-DOPA (tyrosine hydroxylase)
2) L-DOPA–>Dopamine (aromatic AA decarboxylase)
3) Dopamine–>Norepi (dopamine beta-hydroxylase)
Tyrosine, L-DOPA and Dopamine: which cross BBB and which don’t?
Tyrosine and L-DOPA cross BBB; Dopamine does not
Why can’t you treat Parkinson’s patients with dopamine?
it doesn’t cross BBB! Also, oral dopamine will be quickly converted by AAD and COMT so ineffective. Also, low dose can cause orthostatic hypotension, high dose can cause hypertension, tachycardia, nausea and vomiting
What are the cardiovascular effects of dopamine at low dose?
stimulates mesenteric/renal D1 = vasodilation and increased renal blood flow; stimulates presynaptic D2 receptors = decreased alpha1 adrenergic vasomotor tone
What are the cardiovascular effects of dopamine at intermediate dose?
stimulates B-adrenergic in addition to D1; so it will also stimulate myocardial contraction and increase heart rate
What are the cardiovascular effects of dopamine at high dose?
Directly stimulates a1 adrenergic receptors to cause vasoconstriction, inc BP, inc afterload (bad for CHF patient; good only for very low BP circulatory failure ie sepsis/anaphylactic shock)
What dopamine precursor is used to treat Parkinson? What is it’s MOA? What is it used in combo with?
1) Levodopa (L-DOPA)
2) Oral dose absorbed in small bowel and converted to dopamine in periphery by AAD
3) Used in combo with carbidopa
What are some side effects of taking carbidopa and L-DOPA?
Dyskinesias, on-off phenomenon, neuroleptic malignant syndrome, psychosis w/chronic use, (+ hallucinations, GI distress, hypotension, dizziness with L-DOPA)
What are some limitations of dopamine precursor treatment with levodopa/carbidopa?
1) typically effective only for 2-5 yrs (wearing off effect); therefore delay starting tx until older
2) dyskinesias develop after 5-8 yrs
3) “on/off” phenomenon (oscillate between off w/out symptom relief and “on” w/dyskinesia)
What type of drug is Carbidopa? What’s it’s MOA?
Aromatic amino acid decarboxylase inhibitor (AAD inhibitor); it inhibits conversion of L-DOPA to dopamine and doesn’t cross BBB
Compare half lives between carbidopa and levodopa
Levodopa - short half life (1-3hrs); Carbidopa prob more like 4-6 hrs
What is contraindicated with Carbidopa use?
MAO-A inhibitors
What are the two types of Dopamine agonists
Ergot and Non-ergot derivatives
Name 2 Ergot derivatives. Which is no longer used to tx Parkinsons and what’s the reason?
Bromocriptine and Pergolide. Pergolide is no longer used–>causes cardiac valve regurgitation