A Case of Postural Orthostatic Tachycardia Syndrome (POTS) with Difficulties in Differentiation from Hypoglycemic Attack

A 49-year-old man was referred to our clinic for suspected hypoglycemic symptoms of palpitation, cold sweat, faintness and sinking feeling at movement since 43 years old. The 75 g oral glucose tolerance test showed a decrease in plasma glucose to 56 mg/dl at five hours, but this was not associated with clear hypoglycemic symptoms, and normal plasma glucose level recovered naturally after the test. At 48-hour fasting test, plasma glucose dropped to under 50 mg/dl, but the patient didnʼt feel hypoglycemia symptom and plasma glucose recovered naturally, but the patient developed cold sweat and hyperventilation after returning to his own room after the test. At that stage, the heart rate increased to 140 beats/min of sinus tachycardia, as confirmed by Holter monitoring. Postural orthostatic tachycardia syndrome (POTS) was suspected because tachycardia occurred only in daytime after an event such as consumption of diet and urination. A head-up tilt test was ordered since sinus tachycardia developed especially on standing. The results showed an increase in heart rate without reduction in blood pressure, confirming the diagnosis of POTS. A repeat head-up tilt test under the use of a β-blocker showed no increase in heart rate. Though it is generally difficult to distinguish POTS from other forms of tachyarrhythmia, such as inappropriate sinus tachycardia and sinus node reentry tachycardia, and from neutrally mediated reflex syncope (NMS), POTS should be differentiated from hypoglycemia since each condition should be treated differently.