Neuroscience · Year 2 · from Neuroscience
Case 2: Orthostatic Hypotension - Autonomic Failure
Patient Presentation
Demographics: 72-year-old male
Chief Complaint: Recurrent lightheadedness and falls when standing
History of Present Illness: A 72-year-old man with Parkinson's disease diagnosed 8 years ago presents with worsening lightheadedness upon standing, particularly in the morning and after meals. He has fallen three times in the past month when rising from a seated position. He describes near-syncope with graying of vision and weakness in his legs when standing for more than a few minutes. He also reports constipation, urinary hesitancy, and erectile dysfunction that have worsened over the past two years. His Parkinson's disease is treated with carbidopa-levodopa.
Physical Examination:
- Vital signs (supine, after 5 minutes rest): BP 148/88, HR 72
- Vital signs (standing at 1 minute): BP 102/64, HR 76 (inadequate heart rate compensation)
- Vital signs (standing at 3 minutes): BP 88/52, HR 78, patient symptomatic
- General: Masked facies, resting tremor, bradykinesia
- Cardiovascular: Regular rhythm, no murmurs
- Neurological: Findings consistent with Parkinson's disease; no focal deficits
Workup:
- Orthostatic vital signs: Sustained systolic BP drop >30 mmHg without adequate heart rate increase (neurogenic orthostatic hypotension)
- Autonomic reflex testing: Reduced heart rate variability with deep breathing; abnormal Valsalva ratio; absent blood pressure overshoot in phase IV of Valsalva
- Plasma norepinephrine levels: Low in supine position, fail to rise appropriately with standing
- Cardiac MIBG scan: Reduced cardiac uptake (postganglionic sympathetic denervation)
Diagnosis: Neurogenic orthostatic hypotension in Parkinson's disease with autonomic failure
Treatment:
- Non-pharmacological measures: Rise slowly from lying/sitting; compression stockings (waist-high); increased salt and fluid intake (2-3 L water, 10g salt daily); elevation of head of bed 10-20 degrees; small frequent meals; avoid alcohol and large carbohydrate loads
- Midodrine 5 mg three times daily (alpha-1 agonist, titrated based on response)
- Fludrocortisone 0.1 mg daily (volume expansion)
- Droxidopa added for persistent symptoms
- Review of Parkinson's medications (carbidopa-levodopa may worsen orthostatic hypotension)
Clinical Pearl: Neurogenic orthostatic hypotension results from failure of the sympathetic nervous system to appropriately vasoconstrict in response to standing, which normally maintains cerebral perfusion despite gravity-induced blood pooling in the lower extremities. In Parkinson's disease and related synucleinopathies (especially multiple system atrophy), degeneration of sympathetic neurons leads to autonomic failure. The key distinguishing feature from non-neurogenic causes is inadequate compensatory tachycardia (heart rate increase <15 bpm) because the baroreflex arc is impaired.