Differential Diagnosis

The following differential diagnosis is based on the provided symptoms and findings, 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 during the standing test, are consistent with POTS. The diagnosis of POTS has already been made based on the standing test results.
• Other Likely diagnoses
  • Mitochondrial myopathy: The patient's history of high-level rhythmic gymnastics, progressive difficulty with sports, and muscle hypotrophy on ultrasound suggest a possible underlying myopathic condition. The EMG findings of mild low amplitude, short duration, and mild polyphasia also support this diagnosis.
  • Anemia or iron deficiency: The patient's low ferritin levels and history of severe vitamin D deficiency suggest a possible nutritional deficiency contributing to their symptoms.
  • Cardiac autonomic dysfunction: The patient's abnormal heart rate response to exercise and standing test, as well as the diagnosis of POTS, suggest cardiac autonomic dysfunction.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed)
  • Cardiac arrhythmia or conduction disorder: The patient's history of tachycardia, supine and syncope, and abnormal Holter monitoring results necessitate consideration of a potentially life-threatening cardiac arrhythmia or conduction disorder.
  • Pulmonary hypertension: Although the patient's PFTs and inspiratory HRCT are largely normal, the mildly elevated transaminases and significant decrease in exercise tolerance warrant consideration of pulmonary hypertension.
• Rare diagnoses
  • Dysautonomic syndrome: The patient's symptoms, such as orthostatic intolerance, syncope, and abnormal heart rate response, could be consistent with a dysautonomic syndrome, such as familial dysautonomia.
  • Myasthenia gravis: The patient's muscle weakness, particularly in the shoulder girdle, and fatigue could be suggestive of myasthenia gravis, although the EMG findings do not strongly support this diagnosis.
  • Ehlers-Danlos syndrome: The patient's history of joint hypermobility and autonomic dysfunction could be consistent with Ehlers-Danlos syndrome, although this diagnosis would require further evaluation and confirmation.