A 79-year-old New Zealand European woman was referred with an incidental finding of diffuse axial bony sclerosis on a computed tomography (CT) enterography scan that was not present on a CT scan 8 years earlier (Fig. 1). Her past history included a total dental clearance at the age of 16, degenerative disc disease with spinal decompression surgery age 45, a fractured neck of femur at age 75 and generalised bony pain in her shoulders, neck and hip that had progressed over 5 years. Laboratory results showed calcium 2.36 mmol/L (2.10–2.55), phosphate 1.28 (0.75–1.50), alkaline phosphatase 174 IU/L (30–130), normal thyroid function and estimated glomerular filtration rate of 53 mL/min. A bone scintiscan showed diffuse skeletal uptake with no focal lesion. Subsequent investigations revealed a urinary fluoride of 138 μmol/L (0–31) and a fluoride:creatinine ratio of 65.7 μmol/mmol (0–3.1) – confirming the diagnosis of skeletal fluorosis. Fluoride is an essential micronutrient that is rapidly absorbed in the stomach and small intestine, with approximately 50% of an absorbed dose being deposited in mineralised tissue and the rest renally excreted.1 Fluoride alters bone architecture by replacing hydroxyl groups in hydroxyapatite and also stimulates osteoblast activity, resulting in increased bone mass that is radiologically dense but mechanically fragile.1, 2 Clinical manifestations of skeletal fluorosis include bone pain, deformities, fractures and ossification of ligaments and cartilage. The half-life of fluoride in the adult skeleton is estimated at ~7 years.3 Skeletal fluorosis is endemic in areas with high concentrations of fluoride in the drinking water and areas where rock salt with a high fluoride content is also used.4 However, fluorosis is rare in New Zealand, with only one previous possible case reported.5 Our patient lived in an urban area with a fluoride-controlled water supply (0.7–1.0 mg/L) and had no exposure to industrial fumes, fluoride-containing supplements, coal or volcanic fumes. On further history, we elicited that for the past 14 years, she had been drinking 15 cups of Bell Kenya Bold tea per day, each cup made with two tea bags. Prior to this, she drank tea infrequently; but social stressors had led her to increase her intake. Fluoride accumulates in tea plants via absorption from the soil and is stored in the leaves. This particular brand of tea has the highest fluoride concentration of all teas sold in New Zealand, with a single tea bag containing approximately 3.9 mg/L of fluoride when infused into fluoridated drinking water.6 Skeletal fluorosis can occur when daily fluoride intake >10 mg is consumed for over 10 years.3 With our patient's tea consumption, we estimate her intake to have been ~30 mg per day. A 2020 literature review identified 19 cases of non-endemic skeletal fluorosis, half of which were attributed to chronic tea consumption, all in women aged 47–67 years, with the estimated fluoride intake ranging from 13 to 74 mg per day, spanning over 20 years.1 Clinicians should be aware of fluoride as a cause of acquired osteosclerosis and enquire about tea-drinking as a potential source. On follow-up appointments, our patient had managed to reduce her intake by half. The data that support the findings of this study are available from the corresponding author upon reasonable request. Data S1. Supporting Information. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.
Devoe et al. (Sun,) studied this question.