Could this be Refeeding Syndrome?

A young patient who was engaging in heavy weightlifting presented to the ED with proximal muscle weakness. The night before he had one hour of acute onset bilateral leg and hip flexor cramps with stiffness and "hardened" muscles and marked weakness that prevented him from standing or walking. This resolved spontaneously. After an intense workout the next morning he noted cramping and weakness in his legs and was unable to walk, therefore he presented to the ED. 

He had been taking a thyroid supplement for several months but had stopped about three weeks prior. He was also taking lisinopril for hypertension. He was currently using a steroid supplement containing designer steroids (10 mg androstenone and 10 mg androstan-one-azine) for several months. He also took vitamin B5 and niacin. He was eating a high protein diet mainly consisting of chicken and sauce (some sort of Teriyaki sauce) and some rice and very few vegetables for several months averaging 4000 to 8000 calories on most of the days of the week.

Two days before presentation he started eating "normally" again with high amounts of carbohydrates as a treat (cake and sweets).

In the ED: K 2.0 mmol/L, PO4 1.0 mg/dl, glucose 197 mg/dl, Mg 2.0 meq/L, CK 5070 U/L, TSH 0.01, low normal total T3, low total T4 and low free T4 but normal free T3. Urine electrolytes at the time of presentation were notable for a potassium of < 10 and an undetectable phosphorus level (Fractional excretion Phos < 5%). His ECG showed slight abnormalities but troponins were negative x 3.

Phosphate was repleted with 12 mmol NaPhosphate and normalized. Potassium was repleted with 40 meq KCl IV and 120 meq po until normal. His leg weakness resolved and the CK started to trend down.

The question is: what caused his profound electrolyte abnormalities? 

One possibility is refeeding syndrome as described in a previous post. The sudden surge of carbohydrates following a long period of high protein, low carb diet might have caused an increase in insulin driving potassium and phosphate into the cells. Hypomagnesemia was, however, not present in this patient. The time frame (within 4 days) would be consistent with refeeding syndrome. The rhabdomyolysis occurred as a consequence of hypokalemia and hypophosphatemia with a contribution from heavy exercise. He responded quite fast to potassium and phosphate supplementation and improved clinically within a day.

Patients with the following conditions have traditionally been at risk for refeeding syndrome: anorexia, chronic malnutrition (e.g. in patients with cancer), alcoholism, prolonged fasting, after a duodenal switch operation for obesity, hunger strikers and postoperative states. In these times of extreme dieting one should think outside the box and ask about special diets such as high protein diets. The kidney on the other side has been doing it's duty and preserved whatever electrolytes were still in the circulation by absolutely minimizing excretion of potassium and  and phosphate.
Posted by Florian Toegel