A 40-year-old woman, resident of Eastern Uttar Pradesh, India, reported 3 years of low back pain experiencing difficulty walking and 2 years of numbness in legs. On examination, there was dark brown pigmentation on the surface of all her teeth and horizontal brown lines on most of her teeth (figure 1A). She had spastic tetraparesis (strength at shoulder 4/5, legs 4/5) with generally brisk deep tendon jerks, extensor plantar responses and sensory loss below the T1 level. MR scan of the spine showed cervical spinal canal stenosis due to hypertrophy of posterior longitudinal ligament and ligamentum flavum, cervical cord hyperintensity (C3–C5) suggesting cervical myelopathy, and incidental cord compression by T2/T3 disc (figure 1B). X-ray of the pelvis showed calcification of the ilio-lumbar ligament, sacro-iliac and sacro-spinous ligaments and bony sclerosis (figure 1C). X-ray of forearm showed calcification of the interosseous membrane (figure 1D). Her urine fluoride concentration was 2.8 parts per million (normal <1). The fluoride concentration in the underground water that the family consumed was …