What could be causing my constant sinus tachycardia, excessive sweating, and worsening orthostatic hypotension with convulsive syncope on top of my Postural Orthostatic Tachycardia Syndrome (POTS) diagnosis?

Causes of Worsening Symptoms in POTS with Orthostatic Hypotension and Convulsive Syncope

Your symptoms of constant sinus tachycardia, excessive sweating, worsening orthostatic hypotension, and convulsive syncope suggest neurogenic orthostatic hypotension (NOH) complicating your existing POTS diagnosis.

Understanding Your Symptom Complex

POTS is characterized by:

• Heart rate increase ≥30 bpm (≥40 bpm in ages 12-19) within 10 minutes of standing
• Absence of orthostatic hypotension (>20 mmHg drop in systolic BP)
• Symptoms of orthostatic intolerance 1

However, your presentation includes orthostatic hypotension and convulsive syncope, which are not typical POTS features. This suggests additional pathophysiology.

Possible Explanations for Your Symptoms

1. Neurogenic Orthostatic Hypotension (NOH)

   • Defined as dysfunction of the autonomic nervous system causing orthostatic hypotension
   • Distinguished from non-neurogenic causes like dehydration or medications 2
   • Can present with excessive sweating as part of autonomic dysregulation
   • May explain your orthostatic hypotension that's not typical in POTS alone

2. Overlapping Autonomic Disorders

   • POTS can coexist with vasovagal syncope or other forms of reflex syncope 2
   • Convulsive syncope may represent cerebral hypoperfusion severe enough to cause seizure-like activity
   • The excessive sweating suggests hyperadrenergic state or dysautonomia

3. Progressive Autonomic Neuropathy

   • Worsening symptoms could indicate progression of underlying autonomic neuropathy
   • May affect both sympathetic and parasympathetic systems 2
   • Can cause both orthostatic hypotension and inappropriate tachycardia

4. Secondary Causes to Consider

   • Autoimmune disorders affecting autonomic function
   • Parkinsonism or diabetes (associated with delayed orthostatic hypotension) 2
   • Endocrine disorders causing hyperadrenergic state 3

Diagnostic Considerations

Your symptoms warrant investigation for:

1. Autonomic Function Testing

   • Quantitative sudomotor axon reflex test (QSART)
   • Valsalva maneuver and deep breathing tests
   • Pupillary responses 1

2. Blood Tests

   • Complete blood count (anemia)
   • Thyroid function (hyperthyroidism)
   • Catecholamine levels (pheochromocytoma)
   • Autoimmune markers 1

3. Cardiac Evaluation

   • 24-48 hour Holter monitoring
   • Echocardiogram
   • 12-lead ECG 1

Management Approach

Management should target both POTS and neurogenic orthostatic hypotension:

1. For Orthostatic Hypotension

   • Midodrine: Alpha-1 agonist that increases vascular tone and elevates blood pressure
     • Typical dose: 10mg three times daily (last dose before 6pm)
     • Can increase standing systolic BP by 15-30 mmHg 4
   • Volume expansion: Increased salt intake (10-12g daily) and fluid intake (2-3 liters daily) 1
   • Compression garments: Particularly abdominal binders to enhance venous return 1

2. For Tachycardia Control

   • Low-dose beta-blockers (e.g., propranolol)
     • Can help control heart rate and reduce hyperadrenergic symptoms
     • Use with caution as they may worsen orthostatic hypotension 5, 6

3. For Both Conditions

   • Gradual exercise program: Carefully structured to avoid deconditioning 1
   • Avoid triggers: Heat, large meals, prolonged standing 2
   • Fludrocortisone: Helps with volume expansion and BP stabilization 3

Important Cautions

• Beta-blockers can worsen orthostatic hypotension; start at very low doses and monitor closely 5
• Midodrine can cause supine hypertension; avoid taking within 4 hours of bedtime 4
• Convulsive syncope requires careful differentiation from epileptic seizures

When to Seek Immediate Medical Attention

Seek emergency care if you experience:

• Prolonged loss of consciousness
• Injury during syncope episodes
• Severe chest pain
• Sustained palpitations unrelieved by rest
• Shortness of breath at rest 1

Your worsening symptoms suggest progression of autonomic dysfunction beyond typical POTS, requiring comprehensive autonomic evaluation and targeted treatment for both the orthostatic hypotension and tachycardia components.