Osteomalacia secondary to renal tubular acidosis due to Sjögren’s syndrome: a case report and review of the literature

A 43-year-old woman was admitted to our hospital because of generalized bone pain. Arterial blood gas showed pH 7.266, HCO 3 − 13.5 mEq/l, and anion gap (AG) 12. Since her urine pH was 7.0 despite metabolic acidosis with normal AG, we diagnosed distal renal tubular acidosis (RTA). Serum phosphate was 2.5 mg/dl, the level of β2 microglobulin was 41100 μg/l, and aminoaciduria was present. These results indicated proximal tubular dysfunction. The radiograph showed pseudofracture in the pubic bone, indicating osteomalacia. Bone scintigram showed abnormal accumulations of 99mTc-HMDP in multiple joints. Then, her generalized bone pain was considered to be a symptom of osteomalacia. Despite the absence of overt Sicca syndrome, the evaluation of Sjögren’s syndrome (SjS) as a cause of distal RTA was performed. Antibodies to the SS-A level was 127U/ml. Tear break-up time was 3 s bilaterally and salivary gland scintigraphy showed low uptake of 99mTc in the submandibular glands and the parotids. Thus, we diagnosed SjS finally. Gallium scintigraphy showed mild abnormal uptake in bilateral kidneys, suggesting acute tubulointerstitial nephritis. After treatment with prednisolone, alfacalcidol, and sodium bicarbonate, bone pain was remarkably relieved. Additionally, aminoaciduria disappeared and the level of β2 microglobulin decreased. We speculated that the coincidence of proximal tubular dysfunction and distal RTA cause a severe manifestation of osteomalacia.