Autoimmune thyroiditis associated with primary Sjögren’s syndrome complicated with distal renal tubular acidosis and hypokalaemic paralysis: A case report

Abstract

Primary Sjögren's syndrome (pSS) is known to present with distal renal tubular acidosis (dRTA), which can manifest as hypokalaemic paralysis. The main involvement of the kidneys in pSS is tubulointerstitial nephritis. Furthermore, pSS is an autoimmune rheumatological condition that rarely co-exists with autoimmune thyroiditis. We report a 42-year-old hypothyroid female, who complained of a one-day history of severe proximal muscle weakness in all four limbs and a two-month history of left ankle joint pain and swelling. Her serum potassium level was 1.7 mEq/L, with biochemical evidence of normal anion gap metabolic acidosis with positive urinary anion gap suggesting dRTA. As she complained of gritty eyes and recurrent stomatitis a diagnosis of Sjögren's syndrome was sought after. Her serology revealed a high rheumatoid factor titre of 378 (<20) IU/mL with negative anti-cyclic citrullinated peptide levels (<0.5 IU/mL). Positive antinuclear antibodies (1:640), anti-Sjögren's syndrome-related antigen A (SS-A) antibodies and anti-Ro-52 antibodies in the absence of other extractable nuclear antigen antibodies suggested pSS. This was confirmed with labial biopsy which revealed focal lymphocytic infiltration. Magnetic resonance imaging revealed the "salt and pepper" appearance of bilateral parotid glands with glandular atrophy. Even though she was clinically and biochemically euthyroid, given the background of thyroid dysfunction, we investigated for autoimmune thyroiditis (AIT) which was confirmed with imaging and a high anti-thyroid peroxidase antibody titre 532.71 IU/mL (<5.61). Her functional status markedly improved following the correction of serum potassium values. She was started on long term hydroxycholoroquine and oral potassium citrate. This is a rare case of AIT associated with pSS complicated with dRTA presenting with hypokalaemic paralysis. This case illustrates the importance of screening for pSS among patients with dRTA and the rare coexistence of pSS and AIT.Cite this article as: Kalainesan K. et al (2021), Autoimmune thyroiditis associated with primary Sjögren's syndrome complicated with distal renal tubular acidosis and hypokalaemic paralysis: A case report.