HYPERNATREMIC MYOPATHY

We describe a 21-year-old man presenting with proximal muscle weakness associated with hypernatremia. His manifestations other than muscle w eakness included dry skin, loss of axillary and pubic hair, decreased libido and loss of thirst sensation. His serum sodium level was elevat ed to 169-171 mEq./l but all other electrolytes were normal. In additi on, serum CK was elevated and an EMG study showed myogenic changes. En docrinological studies revealed hypothalamic hypopituitarism, while MR I revealed a surprasellar mass. A partial correction of hypernatremia led to an immediate recovery of the muscle weakness as well as a norma lization of both the serum CK level and EMG findings, suggesting a dir ect association between the muscle weakness and hypernatremia. The pho sphocreatine/inorganic phosphorus (PCr/P(i)) ratios in the resting cal f muscle, obtained using P-31 magnetic resonance spectroscopy (MRS), w ere very low during the state of muscle weakness, while they returned to nearly normal values after clinical improvement, suggesting that th e muscle weakness in hypernatremic state was caused by a depletion of the intramuscular energy stores, probably due to an overworking Na-K p ump to correct the intracellular electrolyte imbalance.