Definition and Overview
Autonomic dysfunction in Parkinson's disease (PD) is a non-motor symptom affecting 70-80% of patients. It results from alpha-synuclein accumulation in autonomic ganglia and brainstem nuclei, disrupting sympathetic and parasympathetic regulation [1].
Autonomic symptoms may precede motor symptoms by years (particularly constipation and REM sleep behavior disorder) and significantly impact quality of life.
Manifestations
- Orthostatic hypotension (30-40%): worsened by dopaminergic medications
- Constipation (60-80%): may precede motor symptoms by 10-20 years
- Urinary dysfunction (40-70%): nocturia, frequency, urgency
- Sweating disorders: hyperhidrosis or hypohidrosis
- Sexual dysfunction: erectile dysfunction in 60-70% of men
- Sialorrhea: excessive drooling from reduced swallowing frequency
Diagnosis
MIBG myocardial scintigraphy shows reduced cardiac uptake in PD (denervated sympathetic cardiac neurons), distinguishing PD from MSA where uptake may be preserved [2].
HRV analysis reveals reduced overall variability. Tilt table testing documents orthostatic hypotension. SCOPA-AUT questionnaire screens for autonomic symptom burden [3].
Treatment
Orthostatic hypotension: fludrocortisone, midodrine, droxidopa; adjust dopaminergic medications; non-pharmacological measures (fluids, salt, compression) [4].
Constipation: polyethylene glycol (first-line), dietary fiber, adequate fluids, exercise. Lubiprostone for refractory cases.
Urinary dysfunction: antimuscarinics for overactivity (with caution for cognitive effects); mirabegron as alternative.
Levodopa dose adjustment may be needed as dopaminergic therapy can worsen orthostatic hypotension [5].