【Overview】.
There are two types of hypophosphatemic and hypocalcemic rickets (vitaminD-resi-stantRickets). This section describes the more common hypophosphatemic rickets, also known as familialhypophosphatemia, or renal hypophosphatemic rickets. This disease is characterized by.
(i) low blood phosphorus, which does not respond to normal doses of vitamin D;
(ii) increased urinary phosphorus;
(iii) poor absorption of calcium from the intestine and reduced or normal urinary calcium;
④Symptoms of rickets occur after the first week of age;
⑤ Slow growth, but normal growth in older children.
Etiology
Due to reduced absorption of phosphorus by the renal tubules. The intestinal absorption of calcium and phosphorus is poor, and the blood phosphorus is reduced to 0.65-0.97/mmol/L (2-3mg/dl), and the calcium-phosphorus product is below 30, so the bone is not easily calcified.
The genetics shows a sex-linked dominant inheritance. Male patients can only pass the disease to girls. Female patients can transmit it to both boys and girls. The number of female patients is high, but the symptoms are mild, and most have only low blood phosphorus without obvious rickets skeletal changes. Males have a low incidence, but have more severe symptoms. Occasionally, some cases are autosomal recessive. Some cases are sporadic and there is no family history of the disease.
Clinical manifestations
The symptoms are only discovered when the lower extremities start to bear weight at the age of nearly one year, and the earliest symptoms are often “O”-shaped legs or “X”-shaped legs at the beginning of the disease, while other signs of rickets are very mild. It often goes unnoticed by parents. In more severe cases, there are progressive bone deformities and multiple fractures with skeletal pain, especially in the lower extremities, and even inability to walk. In severe deformities, growth of body length is mostly affected. Poor dental quality, toothache, easy tooth loss and regeneration.
X-rays of bones show varying degrees of rickets, with active and recovering lesions existing simultaneously, most easily detected in the femur and tibia. Laboratory findings are mainly low blood phosphorus, mostly around 0.65 mmol/h (2 mg/dl), while blood calcium may be within normal range or low. Urinary routine and renal function were normal, and there were no amino acids in the urine. The renal tubular reabsorption rate of phosphorus is reduced.
Differential diagnosis
The differentiation between this disease and vitamin D deficiency rickets lies in the following features.
(1) The intake of vitamin D has exceeded the general requirement and active rickets skeletal changes still appear;
②After 2 to 3 years of age, there are still signs of active rickets;
③After giving 400,000 to 600,000 IU of vitamin D orally or intramuscularly, the blood phosphorus of children with general D deficiency rickets rises within a few days and the long bone radiographs show improvement within 2 weeks, while patients with this disease do not have these changes;
④ Hypophosphatemia is common in family members and is characteristic of low phosphorus anti-D rickets.
The disease should also be differentiated from hypocalcemic anti-vitamin D rickets. The latter, also known as vitamin D-dependent rickets, is less common because the kidneys are deficient in 1-hydroxylase and cannot synthesize 1.25(OH)2D. The onset begins a few months after birth and is often accompanied by muscle weakness and early onset of hand and foot tics. Blood calcium is reduced, blood phosphorus is normal or slightly low, blood chloride is increased, and amino aciduria may be present. Although treated with regular doses of vitamin D, rickets still shows signs on X-ray long bone films. It is necessary to increase the amount of vitamin D to 10,000 IU daily or dihyd-rotachysterol (DHT) 0.2 to 0.5 mg to see the effect. Treatment with 0.25-2 μg of 1125(OH)2D3 was found to be curative. The disease is generally autosomal recessive in nature. In addition, this disease must be differentiated from Fanconi’s syndrome and renal tubular acidosis.
Description of treatment
The principle of treatment is to prevent bone deformity and to keep the blood phosphorus as high as possible, above 0.97 mmol/L (3 mg/dl), which is conducive to bone calcification. Maintain the normal growth rate, but also to avoid the occurrence of high urinary calcium and high blood calcium due to vitamin D toxicity. The advantages and disadvantages of various measures are briefly described as follows.
① Oral phosphate alone: In order to raise blood phosphorus to normal levels, phosphate preparations are often required. Generally, 18g of sodium dihydrogen phosphate and 145g of disodium hydrogen phosphate, add water to 1000ml, 15-20ml each time, 5 times a day. 2g of phosphorus (proto-vegetarian phosphorus) daily. Phosphate preparations taste difficult to take and are easily complicated by diarrhea. For better absorption of phosphorus in the intestine it is best to give vitamin D or DHT at the same time.
②Phosphate and vitamin D together: vitamin D dosage 1 to 50,000 IU/day, maximum 100,000 IU/day. Vitamin D is very easy to accumulate in the body fat, until a large amount of storage can be found after the symptoms of poisoning, so it is easy to cause poisoning. DHT is similar to vitamin D products, in the body after hydroxylation of the role of vitamin D, in the body fat is not easy to accumulate, not easy to poisoning, safer. The initial 2 to 4 weeks need to give close to 2mg / d dosage, after only 0.5 to 1.5mg / d maintenance amount can control the disease. After treatment, plasma alkaline phosphatase drops to normal, but blood phosphorus continues to be low, so it should be taken with phosphate preparations. Phosphate preparations of potassium phosphate is more palatable, such as when taken alone may lower the blood calcium. It is better to treat with 1.25(OH)2D30.75-1μg/d plus phosphate.
To prevent excessive blood calcium, 24-hour urine calcium and urine creatinine should be checked every 1 to 3 months. The normal ratio of urinary calcium to urinary creatinine is 0.15 to 0.3. If this ratio is greater than 0.4, the dose of vitamin D or DHT is too high and should be reduced early to reduce the chance of toxicity. Some people advocate the use of diuretics such as dihydrochlorothiazide 1.5 to 2 mg/kg/d, taken orally in divided doses, which can avoid hypercalcemia and can increase blood phosphorus concentration significantly.