Postural orthostatic tachycardia syndrome may not be the first disorder that clinicians consider when they encounter a patient with orthostatic intolerance, but ignoring this possibility during a differential diagnosis can mean patients continue to experience unexplained dizziness, fatigue, syncope, and a variety of other related signs and symptoms. Arriving at the correct diagnosis will allow you to help patients manage the condition and return to the lives and activities they previously enjoyed.
Clinicians should consider postural orthostatic tachycardia syndrome (POTS; ICD-9 code 427.89) as part of the differential diagnosis of orthostatic intolerance (OI). Ignoring this possibility can delay proper diagnosis and treatment among patients who meet the criteria for POTS.
When patients present with symptoms of OI of unknown origin, it is important to consider a broad variety of conditions, including POTS, in the differential diagnosis. Clinicians should follow up with appropriate testing to determine if the criteria for any of these conditions are met. Once the cause of the OI is confirmed, appropriate initial care and referral will facilitate improved treatment for the patient.
A recent consensus statement defines POTS as an increase in heart rate of at least 30 beats/min or a heart rate of at least 120 beats/min upon standing from a supine position—or in response to a tilt-table test—that is sustained for 10 minutes without evidence of orthostatic hypotension.1,2 Although POTS can be seen in men, most cases occur in women of childbearing age, with a female-to-male ratio of 4:1 to 5:1.2 Patients most commonly present with symptoms similar to orthostatic hypotension.3 Typical symptoms include dizziness, near-syncope or syncope, fatigue, headache, visual changes, lightheadedness, weakness, and abdominal discomfort.4,5 Presenting symptoms also overlap with other, more prevalent disorders, leading to frequent misdiagnosis.
Examples of common initial misdiagnoses for patients with POTS include anxiety, chronic fatigue syndrome, fibromyalgia, menopause, orthostatic hypotension, unstable angina, and hyperadrenergic states.1,6 Inappropriate or delayed treatment of POTS can lead to significant daily functional impairment similar to that associated with chronic obstructive pulmonary disease or congestive heart failure.4,6,7
UNDERSTANDING ORTHOSTATIC INTOLERANCE
To better understand POTS, clinicians should have a clear understanding of OI. According to Stewart,8 OI is defined by symptoms of impending near-syncope or syncope, including dizziness, headache, fatigue, exercise intolerance, abdominal distress, or a sensation of feeling “hot” accompanied by sweating. These symptoms occur when a patient assumes an upright position and are relieved when the person returns to a supine position.8
Normally, when a person stands, gravitational forces cause a redistribution of 300 to 800 mL of blood in both the splanchnic and lower extremity circulation. This decreases systolic blood pressure and slows cardiac filling. The resultant decreased cardiac output stimulates increased sympathetic tone via the baroreceptors and other mechanisms to restore arterial blood pressure.1,9 In OI, this compensatory mechanism is compromised, and the patient experiences the symptoms of impending near-syncope or syncope, as discussed previously.
A broad array of medical conditions with multiple etiologies meet the criteria for OI.10 Although a comprehensive list of these conditions is beyond the scope of this article, it is essential for the clinician to look for primary and secondary causes of orthostasis by gathering a comprehensive history, followed by an extensive physical exam directed by the history. The patient should be asked about a history of allergies or autoimmune disease, cancers, eating disorders, infections, adverse effects of medication, and signs or symptoms of chronic sympathetic stimulation. It is also important to review the current medication list carefully and evaluate the patient for dysfunction of the cardiac, endocrine, renal, and nervous systems and for psychiatric disorders. A short list of conditions that may present with OI include anemia, anorexia, autoimmune disease, cancers, cardiac disease, diabetes, infections, paraneoplastic syndromes, vascular disease, and volume depletion.2,8,11,12
Hypotension is absent in POTS, but it otherwise also fits the profile of OI. POTS can also present with a host of other nonspecific, nonorthostatic symptoms, including nausea, vomiting, diarrhea, constipation, fatigue, migraine headaches, and chest pain.10 This unusual presentation can confound the clinician and complicate the medical picture, making a clear diagnosis difficult.
On the next page: History, epidemiology, and etiology >>