Overview
Definition:
Orthostatic intolerance (OI) is a condition characterized by the development of symptoms upon assuming an upright posture that are relieved by lying down
It represents a failure of the autonomic nervous system to adequately compensate for the gravitational shift of blood volume to the lower extremities upon standing.
Epidemiology:
OI is common in adolescents, particularly in young women
Prevalence estimates vary, but it is a significant cause of recurrent syncope and presyncope in this age group
It can significantly impact quality of life and school attendance.
Clinical Significance:
OI can lead to recurrent syncope or near-syncope, impairing daily activities, academic performance, and social participation
Early recognition and management are crucial to prevent injuries from falls and improve patient well-being
Understanding the role of fluids, salt, and exercise is central to its conservative management.
Clinical Presentation
Symptoms:
Symptoms typically develop within minutes of standing
Common symptoms include lightheadedness or dizziness
Palpitations
Blurred vision or tunnel vision
Nausea
Fatigue
Headache
Weakness or shakiness
Feeling of heat or flushing
Inability to concentrate
Symptoms are relieved by sitting or lying down.
Signs:
On standing, a significant drop in systolic blood pressure (>20 mmHg) or diastolic blood pressure (>10 mmHg) may be observed, often accompanied by a significant rise in heart rate (>10-20 beats per minute in younger individuals, or >30 beats per minute in adults)
However, some individuals, particularly those with hyperadrenergic POTS, may not demonstrate a significant drop in blood pressure but still experience symptoms.
Diagnostic Criteria:
While specific diagnostic criteria for OI in adolescents can be nuanced, the hallmark is symptom exacerbation in the upright posture and relief in the supine position
Formal diagnosis often involves a tilt table test, which can confirm the hemodynamic response to postural changes
Postural Orthostatic Tachycardia Syndrome (POTS) is a specific subtype of OI characterized by a sustained heart rate increase of at least 30 bpm (or 40 bpm in adolescents) within 10 minutes of standing, in the absence of orthostatic hypotension.
Diagnostic Approach
History Taking:
Detailed history is paramount
Ask about symptom onset, duration, frequency, and triggers
Inquire about posture-related symptoms, syncope, presyncope, palpitations, and associated symptoms
Obtain a thorough past medical history, including any history of viral illness or trauma, which can be triggers
Review medications
Identify any red flags such as neurological deficits, chest pain, or exertional dyspnea.
Physical Examination:
Perform a thorough cardiovascular and neurological examination
Measure blood pressure and heart rate in both supine and standing positions (standing 1 and 3 minutes)
Assess for signs of dehydration, anemia, or thyroid dysfunction
Neurological examination should rule out other causes of dizziness or syncope.
Investigations:
A basic laboratory workup may include a complete blood count (CBC) to rule out anemia, serum electrolytes and renal function tests to assess hydration and electrolyte balance, and thyroid function tests
An electrocardiogram (ECG) is essential to rule out cardiac causes of syncope
Holter monitoring may be considered if arrhythmias are suspected
A tilt table test is the gold standard for confirming OI and categorizing the type (e.g., neurally mediated syncope, POTS, orthostatic hypotension).
Differential Diagnosis:
Differential diagnoses for orthostatic intolerance include vasovagal syncope, orthostatic hypotension (due to hypovolemia, autonomic neuropathy, or medications), cardiac arrhythmias, pulmonary embolism, anemia, hypoglycemia, and neurological conditions like seizures or vestibular disorders
It is important to distinguish OI from these conditions.
Management
Initial Management:
Lifestyle modifications are the cornerstone of management
These include increasing fluid and salt intake, gradual increase in physical activity, and avoidance of triggers such as prolonged standing, heat, and dehydration.
Medical Management:
Pharmacological interventions are considered when lifestyle modifications are insufficient
For POTS, beta-blockers (e.g., propranolol 0.5-1 mg/kg/day divided BID) can help control tachycardia
Midodrine (0.2 mg/kg/day divided TID, max 1 mg/kg/day) may be used for orthostatic hypotension
Fludrocortisone (0.1 mg once daily) can increase blood volume by promoting salt and water retention
Other agents like pyridostigmine and selective serotonin reuptake inhibitors (SSRIs) may be considered in specific cases
Always titrate doses carefully and monitor for side effects.
Surgical Management:
Surgical management is generally not indicated for orthostatic intolerance
The focus is on conservative and medical therapies.
Supportive Care:
Education and psychological support are vital
Patients and families need to understand the condition, its triggers, and management strategies
Encourage adherence to treatment plans
Regular follow-up appointments are necessary to monitor symptoms, adjust medications, and assess for complications.
Complications
Early Complications:
Falls and subsequent injuries are the most common early complications, particularly during syncopal episodes
Severe symptoms can lead to dehydration if fluid intake is poor.
Late Complications:
Chronic symptoms can lead to significant psychosocial impact, including social isolation, depression, anxiety, and impaired academic and occupational functioning
Persistent fatigue and deconditioning can occur if not managed effectively.
Prevention Strategies:
Preventing falls involves patient education on recognizing prodromal symptoms and taking immediate action (e.g., sitting or lying down)
Ensuring adequate hydration and electrolyte balance, and gradual, progressive exercise are key preventive strategies
Careful medication titration and monitoring also reduce the risk of adverse events.
Prognosis
Factors Affecting Prognosis:
The prognosis for OI in adolescents is generally good, with many experiencing significant improvement or resolution of symptoms over time, especially with consistent adherence to lifestyle modifications and appropriate medical management
Factors influencing prognosis include the underlying cause of OI, severity of symptoms, patient adherence, and timely intervention.
Outcomes:
With comprehensive management, most adolescents can achieve a significant reduction in symptoms, allowing them to return to normal activities, school, and sports
Complete resolution is possible for many, though some may experience chronic intermittent symptoms.
Follow Up:
Regular follow-up with a pediatrician or pediatric cardiologist is recommended to monitor symptom control, adjust treatment as needed, and address any emerging complications
Follow-up frequency will depend on symptom severity and treatment response, typically ranging from every 3-6 months initially.
Key Points
Exam Focus:
Remember the role of fluids, salt, and exercise as first-line management for OI in adolescents
Be familiar with the hemodynamic criteria for POTS on tilt table testing
Understand common pharmacologic agents and their indications/dosing.
Clinical Pearls:
Emphasize patient education
adherence to fluid and salt intake is often challenging but crucial
A gradual exercise program, often starting with recumbent exercises, is more effective than complete inactivity
Consider OI in any adolescent presenting with recurrent syncope or severe fatigue impacting daily life.
Common Mistakes:
Mistake: Over-reliance on medications without addressing lifestyle factors
Mistake: Aggressive exercise initiation that exacerbates symptoms
Mistake: Failing to consider and rule out other serious causes of syncope
Mistake: Underestimating the psychosocial impact of chronic OI.