Snapshot A 6-year-old boy is brought to his pediatrician by his parents due to poor growth, weakness, and abnormal gait. On physical exam, there is bowing of the legs and tenderness upon palpation of the lower extremity. Laboratory testing is significant for a decreased serum calcium and phosphate levels and elevated parathyroid hormone and serum alkaline phosphatase levels. (Rickets secondary to vitamin D defiency) Introduction Clinical definition osteomalacia a condition due to defective mineralization of osteoid rickets a condition due to defective mineralization of cartilage in the epiphyseal growth plates Epidemiology Demographics children can have both osteomalacia and rickets adults can only have osteomalacia since their growth plates have been fused Risk factors vitamin D deficiency secondary to poor dietary intake and sun exposure malabsorption e.g., inflammatory bowel disease and gastrointestinal bypass surgery genetic causes that result in vitamin D deficiency and vitamin D resistance primary hypophosphatemia e.g., X-linked hypophosphatemic rickets and autosomal dominant hypophosphatemic rickets Etiology Vitamin D deficiency Hypophosphatemia Chronic kidney disease e.g., metabolic acidosis and decreased 1,25-dihydroxyvitamin D synthesis Renal tubular acidosis proximal (type II) renal tubular acidosis/Fanconi syndrome secondary to phosphate wasting, metabolic acidosis which increases calcium loss, and secondary hyperparathyroidism Inhibitors of bone mineralization e.g., bisphosphonates, alimunum, and fluoride Hypophosphatasia a tissue non-specific alkaline phosphatase (TNSALP) gene mutation that leads to the accumulation of pyrophosphate pyrophosphate inhibits bone mineralization Pathogenesis impaired mineralization of osteoid (osteomalacia) and/or cartilage at the epiphyseal plates (rickets) Presentation Symptoms bone and joint pain muscle weakness difficulty with walking fractures Physical exam pediatric bowed legs rachitic rosary line costochondral thickenings Harrison's groove depression along line of diaphragmatic insertion into rib cage kyphosis as well as lordosis and scoliosis poor growth bone tenderness to palpation Imaging Radiography indication perform in patients with a clinical presentation concerning for osteomalacia or rickets findings osteomalacia reduced bone mineral density a non-specific finding inability to radiologically distinguish vertebral body trabeculae the film appears poor quality Looser pseudofractures, fissues, or narrow radiolucent lines characteristic radiologic findings rickets perform an anteriorposterior radiograph in skeletal areas that are rapidly growing (e.g., knee or wrist) osteopenia metaphysis may appear frayed and widened distal physis may appear widened bones of the arms and legs may have angular defomities Studies Labs highly dependent on the cause e.g., patients with vitamin D deficiency will have decreased 25-hydroxyvitamin D Laboratory Abnormalities in Rickets/OsteomalaciaEtiologySerum PhosphateSerum CalciumSerum Alkaline PhosphataseParathydroid HormoneVitamin D deficiency Decreased or normal Decreased or normal Elevated ElevatedUrinary phosphate wasting Decreased Normal Elevated or normal NormalProximal (type II) renal tubular acidosis Decreased Normal Normal NormalHypophosphatasia Normal Normal Decreased Normal Differential Child abuse Osteogenesis imperfecta Osteoporosis Paget disease of bone Multiple myeloma Vitamin D resistant rickets normal vitamin D and normal PTH Laboratory Abnormalities in Select Bone DisordersEtiologySerum PhosphateSerum CalciumSerum Alkaline PhosphataseParathyroid HormoneOsteoporosisNormalNormal or decreasedNormalNormalPaget disease of the boneNormalNormalElevatedNormalOsteitis fibrosa cysticaPrimaryhyperparathyroidism •decreasedSecondaryhyperparathyroidism •increasedPrimaryhyperparathyroidism •increasedSecondaryhyperparathyroidism •decreasedPrimary and secondary hyperparathyroidism •increasedPrimary and secondary hyperparathyroidism •increasedHypervitaminosis DIncreasedIncreasedNormalDecreased Treatment Medical treatment is directed against the underlying cause for example vitamin D supplemention indication in patients with vitamin D deficiency hereditary hypophosphatemic rickets along with phosphate supplementation osteomalacia of renal tubular acidosis along with sodium or potassium citrate Complications Fractures Growth abnormalities Prognosis Depends on the etiology