We made a diagnosis of distal RTA on the basis of severe hypokalemia, urinary loss of potassium (>15 mEq/l), hypercalciuria, normal anion gap metabolic acidosis and alkaline urine.2
Normal linear growth and severe weight loss suggested an acute insult. Furthermore, there was no nephrocalcinosis and long standing RTA seemed unlikely. Although rare, a dominant form of distal RTA may present in adolescents and be milder than disease presenting in infancy.3
The SMA artery syndrome describes extrinsic compression of the duodenum causing obstruction and occurs in children after rapid weight loss and is most marked when they lie supine. The compression may occur when the mesentery loses fat and allows the SMA to compress the duodenum, between the SMA anteriorly and the aorta posteriorly. Alternatively, loss of supporting fat in the second and third portions of the duodenum may allow the duodenum to collapse against the spine.4
A classic example is an adolescent who starts vomiting after application of a body cast for orthopaedic surgery. Other factors include anorexia, prolonged bed rest, weight loss, abdominal surgery and exaggerated lumbar lordosis. The diagnosis is established radiologically with the demonstration of a cut-off of the duodenum just to the right of the midline. The duodenal obstruction may be accompanied by proximal duodenal and gastric dilatation.4
In this child, there was no evidence of obstruction and her vomiting could not be attributed to SMA syndrome, which may have been due to loss of weight and her slim habitus.
Intractable recurrent vomiting in a child should prompt a search for both obstructive and non-obstructive causes.
- Metabolic acidosis in presence of severe hypokalemia suggest RTA, diarrhoea or diabetic ketoacidosis as possible diagnoses.
- Normal Anion gap acidosis and alkaline urine indicates distal RTA.
- Rarely, RTA may present late.
- Ultrasonic features of SMA may be found in thin children, who have lost weight and mesenteric or retroduodenal fat but this may not be responsible for symptoms.