Distal renal tubular acidosis - An unexplained distal RTA is a invitation to investigate for Sjogren's. Patients with distal RTAs are prone to nephrolithiasis (typically calcium phosphate stones) and nephrocalcinosis. Severe associated hypokalemia can also occur with flaccid paralysis having been described as a presenting symptom.
Although the cause of distal RTAs in most patients with Sjogren's syndrome is unknown a few patients have been described who have an absence of the H-ATPase pump on intercalated cells in the collecting duct. Another hypothesis is that Sjogren's leads to autoantibodies directed against carbonic anhydrase II thus leading to the generation of less protons for excretion.
Proximal RTA and full blown Fanconi's syndrome have also been described.
Nephrogenic diabetes insipidus - Urinary concentrating defects are not uncommon in patients with Sjogren's. As an example, in an Italian series 21% of patients were noted to have an abnormal urinary concentrating ability. The cause of this tubular defect is again unknown but histologically clusters of lymphocytic infiltrate can sometimes be seen around collecting ducts which could theoretically interfere with the actions of ADH.
Hypokalemia - This can occur in the absence of RTA and is thought to be due to tubular damage induced sodium wasting with subsequent increased distal sodium delivery. In the distal nephron increased sodium delivery drives potassium loss in exchange for sodium. This effect may be amplified by volume depletion with subsequent increased aldosterone levels which again drive sodium absorption and potassium loss.