Parkinson’s Disease

Associated pages:
Essential Tremor

FACTS

Nigro-striatal pathway

  • projects from substantia nigra pars compacta to striatum.
  • differential activation of each pathway is via D1 (direct) and D2 (indirect) receptor activation.
  • direct and indirect pathways of striatal medium spine neurons (MSNs).
Path
Function
Receptor
Details
Direct
Excitatory (initiation)
D1
cortex -> Striatum -> GPi -> thalamus -> motor cortex -> s.c / brainstem
Indirect
Inhibitory (termination)
D2
cortex -> striatum -> GPe -> STN -> GPe -> thalamus -> motor cortex -> spinal cord / brainstem
Feature
Essential Tremor
Parkinsonian Tremor
Cerebellar Tremor
When
Action / Postural
Rest
Intention (during goal-directed movement)
Amplitude
Fine to medium
Coarse
Broad, irregular
Frequency
6–12 Hz (faster)
4–6 Hz
2–4 Hz (slow)
Distribution
Hands, head, voice
Hands, chin, legs
Limb (often unilateral), truncal
Alcohol effect
Improves
No effect
No effect
Tone
Normal
Increased (rigidity)
Normal or hypotonic
Gait
Normal
Shuffling
Ataxic
DBS Target
VIM, less commonly posterior subthalamic nucleus (PSA)
GPi, STN
-

HPI

Cardinal symptoms (responsive to DBS/levodopa):
  • resting tremor
  • rigidity
  • bradykinesia
Other Sx
freezing
falling
dysarthria
cognitive decline
bowel/bladder dysfunction

PHYSICAL EXAM

Rest tremor

IMAGING

None
A/P
Therapies that only address cardinal symptoms of PD
  1. Levodopa is first trial therapy
  1. DBS once refractory to levodopa
 

Globus Pallidus Interna (GPi)

notion image
  • GPi adjacent structures
    • inferior: optic tract
    • medial: internal capsule
    • medial/superior: thalamus
    • medial/inferior: STN, substantia nigra
  • visual obscurations during awake testing confirm adequate placement (which would be slightly shallower)