A Case of Renal Tubular Acidosis with Sjogren's Syndrome Showing Paradoxical Block of PTH Due to Severe Hypomagnesemia.

Distal renal tubular acidosis (RTA) manifests either as Complete/Classical form or Incomplete/Latent Form. Distal RTA causes normal anion gap metabolic acidosis and hypokalemia. Interstitial Nephritis is the most frequent renal manifestation of Sjogren's, which presents as Distal RTA in 25-40% of patients with Sjogren's syndrome. Magnesium deficiency is frequently associated with hypokalemia. Although serum calcium is the main physiological control for the secretion of parathyroid hormone (PTH) by the parathyroid, serum magnesium can also exert similar effects. While low levels of magnesium stimulate the secretion of PTH, very low serum concentrations tend to induce a paradoxical block of PTH release by activation of the alpha-subunits of heterotrimeric G-proteins. This mimicks the activation of calcium sensing receptor leading to inhibition of PTH secretion. Here we describe the case history of a 35-year-old lady who presented to our hospital with severe hypokalemia due to distal RTA and perhaps had a paradoxical block of PTH secretion in the setting of severe hypomagnesemia.