Clinical history

A 30-year-old taxicab driver presented with a 1-year history of low back pain radiating into the posterior aspect of both legs, stiffness during inactivity, and proximal upper and lower limb myalgia. Symptoms were poorly controlled with acetaminophen. The medical history was unremarkable. The patient was a vegetarian, smoked 5 cigarettes per day, and did not drink alcohol. He was born in the Punjab region of southern Asia and had lived there until moving to the United Kingdom at the age of 25 years. Physical examination findings included globally restricted movement of the lumbar spine, sacroiliac joint tenderness, grade 4/5 proximal muscle weakness, and inability to rise from a chair with folded arms. Neurologic findings were otherwise normal.

Serum biochemistry studies revealed the following: alkaline phosphatase 164 units/liter (normal <125), elevated bone isoenzyme levels, alanine transaminase 68 units/liter (normal <40), normal levels of bilirubin and gamma glutamyl transpeptidase, corrected calcium 2.42 mmoles/liter (normal 2.15–2.55), phosphate 0.65 mmoles/liter (normal 0.75–1.5), parathyroid hormone 6.5 pmoles/liter (normal 1.1–6.5), and 25-hydroxyvitamin D 14 nmoles/liter (normal 20–100).

Radiologic findings

Radiographs revealed no features of osteomalacia, but diffuse sclerosis and calcification of both entheseal and joint capsules were seen (Figures 1 and 2). These findings were characteristic of fluorosis. Serum and urine fluoride levels were thus measured; these levels were 146 mg/liter (normal 6–45) and 0.7 mg/liter (normal ,1.6), respectively. Bone mineral density in the lumbar spine (L1–L4) was 2.284 gm/cm2, with a T score of 19.20 and a Z score of 18.87.

The radiologic differential diagnosis of diffuse bone sclerosis included osteopetrosis, mastocytosis, myelofibrosis, prostatic metastases, renal osteodystrophy, hypoparathyroidism, and certain hemoglobinopathies, particularly sickle cell disease. The radiologic differential diagnosis of entheseal calcification included seronegative spondylarthropathy, diffuse idiopathic skeletal hyperostosis, calcium pyrophosphate deposition arthropathy, hypoparathyroidism, and X-linked hypophosphatemic osteomalacia.

Transiliac bone biopsy (Figures 3 and 4) revealed increased cancellous bone volume (36.5%; age-matched normal ,23%), areas of woven mineralized bone, increased bone surface covered by osteoid (40%; age-matched normal <15%), and increased osteoid thickness (average 6–12 lamellae; age-matched normal <3); most tetracycline- and oxytetracycline-stained surfaces showed single labels (results not shown).