Differential Diagnosis

The following list provides a neutral differential diagnosis based on the provided information, without assuming any cause or suggesting treatment.

• Single most likely diagnosis

  • Postural Orthostatic Tachycardia Syndrome (POTS): The patient's symptoms, such as rapid fatigue, shortness of breath on exertion, occasional syncope, and a significant increase in heart rate upon standing (52 bpm), along with a diagnosis of POTS from the standing test, make this a highly likely diagnosis. The patient's history of tachycardia, supine and syncope hospitalizations, and the findings from the Holter monitor and stress ECG also support this diagnosis.

• Other Likely diagnoses

  • Mitochondrial Myopathy: The patient's progressive difficulty with sports, rapid fatigue, and shortness of breath on exertion, along with muscle hypotrophy and mild low amplitude, short duration, mild polyphasia on EMG, suggest a possible mitochondrial myopathy. The patient's underweight status and decreased appetite over time also support this diagnosis.
  • Anemia: The patient's low ferritin levels and history of severe vitamin D deficiency may contribute to anemia, which could explain some of the patient's symptoms, such as fatigue, shortness of breath, and decreased exercise tolerance.
  • Cardiomyopathy: Although the echocardiogram is normal, the patient's symptoms of tachycardia, supine and syncope, and the findings from the stress ECG and Holter monitor, may suggest a possible cardiomyopathy.

• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)

  • Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC): Although the echocardiogram is normal, the patient's symptoms of tachycardia, supine and syncope, and the findings from the stress ECG and Holter monitor, may suggest a possible ARVC. This condition can be life-threatening if not diagnosed and treated promptly.
  • Pulmonary Embolism: The patient's shortness of breath on exertion and decreased exercise tolerance may suggest a possible pulmonary embolism, which can be life-threatening if not diagnosed and treated promptly.
  • Cardiac Sarcoidosis: The patient's symptoms of tachycardia, supine and syncope, and the findings from the stress ECG and Holter monitor, may suggest a possible cardiac sarcoidosis. This condition can be life-threatening if not diagnosed and treated promptly.

• Rare diagnoses

  • Duchenne Muscular Dystrophy: Although the patient's EMG and muscle ultrasound findings do not suggest a typical muscular dystrophy, the patient's progressive muscle weakness and fatigue may suggest a possible rare form of muscular dystrophy, such as Duchenne muscular dystrophy.
  • Kearns-Sayre Syndrome: The patient's symptoms of progressive external ophthalmoplegia, muscle weakness, and fatigue, along with the findings from the EMG and muscle ultrasound, may suggest a possible Kearns-Sayre syndrome, a rare mitochondrial myopathy.
  • Myasthenia Gravis: The patient's muscle weakness and fatigue may suggest a possible myasthenia gravis, a rare autoimmune disorder that affects the neuromuscular junction.