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Sjögren’s syndrome (SjS) is a chronic autoimmune connective tissue disease that mainly affects the lacrimal and salivary glands. The immune process can also affect nonexocrine organs including the kidneys. Renal involvement in SjS is the most commonly encountered extraglandular manifestations. The most frequent form of nephropathy in SjS is tubulointerstitial nephritis, such as renal distal tubular acidosis (dRTA) and diabetes insipidus. A defect in distal acidification occurs in up to 25% of patients with SjS. Patients may present with a dRTA without a prior diagnosis of SjS and hydroelectrolyte disorders can be the first symptom of renal disease, including severe hypokalemia, which may cause muscle paralysis.
A 42 year old female patient sought the emergency unit in January 2022, reporting sporadic muscle weakness of the upper limbs that had began 15 days ago, with significant worsening in the last 24 hours. On physical examination, the patient had speech difficulties, quadriparesis and glasgow coma scale of 15. Laboratory tests showed severe hypokalemia, hypernatremia, hyperchloremic metabolic acidosis and preserved renal function. Patient underwent brain CT scan, in addition to liquor puncture. MRI of the neck, chest and abdomen were performed, all ot them without any abnormalities. Patient was sent to the intensive care unit (ICU) hemodynamically stable, normoglycemic, with marked polyuria (9.4L in 24 hours). On the 13th day of hospitalization, she developed bradycardia with the need of atropine. After 17 days in the ICU, the patient showed an improvement in hydroelectrolyte leves and was able to walk with support, but remained polyuric. A Nephrologist was finally requested. Complete screening for tubulopathy was performed and dRTA with nephrogenic diabetes insipidus was diagnosed. Appropriate therapy was immediatly instituted. Outpatient tests were positive for SjS.
Results
The patient's clinical manifestations included severe muscle weakness in upper and lower extremities with acid-base and hydroelectrolyte disorders. She also had polyuria. dRTA is characterized by impaired hydrogen (H+) ion secretion in the distal nephron, which reduces the kidney's ability to excrete the daily acid load. This results in progressive H+ ion retention and a hyperchloremic metabolic acidosis. dRTA is commonly associated with hypokalemia due to renal potassium wasting. Occasionally, the hypokalemia is so severe that it results in muscle paralysis or respiratory arrest. The major causes of new-onset dRTA in adults are autoimmune diseases, such as SjS. The exact mechanism remains unclear. However, previous studies evidenced a downregulated expression of the vacuolar H+-ATPase in the A-intercalated cells in patients with SjS with concomitant underexpression of AE1 (pendrin) in the B-intercalated cells. Arginine vasopressin resistance leading to polyuria and polydipsia is another potential manifestation of impaired tubular function in SjS.
Autoimmune diseases are important causes of distal renal tubular acidosis in adults. It is not uncommon for renal tubular acidosis lead to the diagnosis of SjS, and it can occur even years before the disease becomes clinically established. Therefore, in the face of hipokalemic paralysis, dRTA must be considered and the possibility of the presence of SjS should not be disregarded. The late diagnosis may be fatal.