Back pain in chronic renal failure

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Patient SK, a 40-yr-old female, resident of Bhagalpurvillage in Bihar, India, was operated for gallstones3 years previously. On pre-operative checkup, mildrenal dysfunction was detected. She was asymptomaticfor renal disease with serum creatinine of 159mmol/l(1.8mg/dl), bland urinary sediment and small echo-genic kidneys on ultrasound. She was puton conservative management for chronic renal failure(CRF) and was doing well till 1 year ago. Since thenshe developed back pain, which increased on walking.Pain was dull in character without any radiation. Therewere no systemic complaints. In the past month whenher pain increased substantially, causing discomfort inday-to-day activities. On investigation she was foundto have moderate renal failure with blood ureanitrogen (BUN) of 11.8mmol/l and serum creatinineof 309mmol/l (3.5mg/dl). Other labs showed serumcalcium of 2.4mmol/l, phosphorus 1.1mmol/l, alkalinephosphatase 243U/l, uric acid 381mmol/l and intactparathyroid hormone (iPTH) of 182.0pg/ml. X-raysof bilateral forearms, pelvis and spine were taken(Figures 1–3, respectively), which revealed generalizedincrease in bone density, degenerative changeswith osteophytes in lumber vertebra, calcification ofbilateral iliolumbar and sacrospinous ligaments andinterosseous membrane calcification in forearms.Definitive diagnosis was reached with estimation offluoride levels in blood and urine, which were0.291mg/l and 0.962mg/l (15.3 and 50.6mmol/l),respectively. Her drinking water source, ground waterfrom a tubewell, was found to contain 3.910mg/l(205.9mmol/l) of fluoride. She was diagnosed to havefluorosis with moderate CRF and was advised to usedomestic reverse-osmosis-treated water for cookingand drinking.Main sources of fluoride include food and water.About 50–70% of fluoride is excreted by the kidneys[1]. Individuals with kidney disease have decreasedability to excrete fluoride in urine and are at risk ofdeveloping fluorosis even at normal recommendedlimit of 0.7 to 1.2mg/l (37–63mmol/l) of fluoride indrinking water [2]. In fluorosis with normal renalfunction, urine fluoride rises above 0.5–4.48mg/l(26–236mmol/l) and may reach 1.5–13.0mg/l(79–685mmol/l) [3]. Serum fluoride rises to0.04–0.28mg/l (2.1–14.7mmol/l) in such patients [1].Fluoride is bone-seeking due to its high affinity forcalcium phosphate and therefore accumulates in bone.Radiological changes can be quite similar to changesof renal osteodystrophy, and therefore the diagnosismay be missed unless specifically investigated.