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Definition and Epidemiology of Rickets
According to standard textbooks, rickets is the imperfection, distortion, and softening of the bones due to vitamin D deficiency. Vitamin D, which is fat-soluble, is essential for the body.
Since the leading cause of rickets is vitamin D deficiency, and Vitamin D is a hormone that is synthesized upon exposure to sunlight, the disease is more prevalent in regions where people have less exposure to sunlight. The growth spurt, especially in puberty, is one reason for the manifestation of rickets.
A diet with low vitamin D and calcium intake is also linked to the development of rickets. While rickets is rare in developed countries, it is frequent in children in developing countries. Poverty and inadequate availability of food are also reasons for the development of rickets in children.
Etiology and Classification of Rickets
Vitamin D is a fat-soluble hormone responsible for maintaining serum phosphate and calcium levels, which, in turn, are of foremost importance for bone mineralization. Exposure to sunlight causes the conversion of vitamin D from its inactive to the active form in skin cells.
The primary reason for congenital rickets is maternal vitamin D deficiency. Vitamin D is transported in the form of 25 hydroxyvitamin D from the mother to the fetus through the placenta.
The risk factors for vitamin D deficiency in neonates include:
- Maternal vitamin D deficiency during pregnancy
- Prolonged breastfeeding without vitamin D supplementation
- Dark skin complexion: Individuals whose ancestors evolved in northern latitudes may have a selection for lighter skin that allows UV rays to produce Vitamin D from 7-dehydrocholesterol. Darker skin can block most UV radiation to prevent toxic levels of Vitamin D, as well as skin cancer
- Very low sun exposure
Also, both gastroenterological interventions that remove the lower part of the small bowel where Vit D is absorbed and intestinal diseases that impair the normal absorption decrease vitamin D uptake, even with adequate nutritional supplementation.
The primary reason for rickets in children is vitamin D deficiency. Vitamin D is synthesized by exposure to sunlight. Insufficient exposure to sunlight and certain dietary habits, like a diet exclusively based on grains, are biological reasons for the development of rickets in children.
In some cases, there may be a normal level of vitamin D but a decrease in activity due to a lack of conversion to the active metabolite or the receptor’s resistance to the metabolite. This results in what is known as calciopenic rickets.
There is also a genetic cause for rickets, known as vitamin D resistant rickets (X- linked hypophosphatemia). It can occur because of phosphate deficiency, which has been reported as a cause of rickets in children.
The broad categories of rickets consist of:
Vitamin D-related rickets
- Vitamin D deficiency leading to rickets
- Vitamin D dependent rickets
- Type 1: deficiency of the 1-alpha-hydroxylase enzyme
- Type 2: a mutation in the calcitriol receptor
- Due to direct hypocalcemia
- Due to hypoparathyroidism, chronic renal failure (as the kidneys are responsible for the activation of vitamin D and help in the reabsorption of calcium), or malabsorption
- Congenital hyperphosphatemia
- Autosomal dominant hypophosphatemic rickets
- Autosomal recessive hypophosphatemic rickets
- Vitamin D-resistant rickets
- Secondary to malabsorption
- Fanconi syndrome, a syndrome of inadequate reabsorption in the proximal renal tubules of the kidney, causing phosphate loss
Rickets secondary to other diseases
- In addition to this, rickets might arise secondary to other diseases, such as epidermal nevus syndrome and McCune Albright syndrome.
Pathophysiology and Symptoms of Rickets
Calcium is absolutely essential for the mineralization of the chondrocytes, which are formed in the growth plate. In calcium deficiency, though there are proliferation and hypertrophy of chondrocytes, the concurrent invasion by the vascular tissue and the conversion of the formed chondrocytes into a mineralized structure is deficient.
This results in a disorganized growth plate and proliferative zone expansion. Ultimately, bone stability is severely compromised, leading to bowing and other characteristic features of rickets. The symptoms are very common among children.
- The fontanelles are present at the junction of the skull bones. In individuals with rickets, there is a delay in the time of closure of fontanelles. Since there is deficient mineralization in the skull bones, there is bossing due to pressure from the underlying brain, which is especially prominent in the parietal and frontal regions.
- Both Genu varum, as well as Genu valgum, can occur depending on the age at which the rickets manifest. In cases of rickets in toddlers, Genu Varum occurs; in older children, Genu valgum occurs.
- The disease can cause spinal deformity (kyphoscoliosis) and an increased risk of tetany.
- The skull bones are soft, a condition known as craniotabes.
- The ribs are not strong enough to support the pull, which occurs during respiration. This results in the formation of a characteristic sulcus, which is present at the lower margin of the chest, known as Harrison sulcus.
- The distal bones broaden, especially the upper arm bones (radius and ulna) and the lower arm bones (tibia).
- The proliferation of chondrocytes in rickets manifests as the enlargement of the costochondral junction, which forms characteristic beading along the chest, known as a rachitic rosary, and there also is widening of the wrists.
- The bones are tender, there are problems with the dental architecture. Greenstick fractures occur, and there is increased muscle weakness, affecting growth.
Progression and Complications of Rickets
The progression of rickets leads to the bowing of both the legs with the development of Genu valgum. Growth is also severely stunted if rickets occurs at younger ages. Genu valgum is a characteristic known as knock knees, where the knees are basically angled in.
The greatest interference with the growth of the child happens when the onset of rickets is at a younger age, leading to short stature. Chronic rickets also leads to the development of osteoarthritis and other degenerative bone disorders. Ultimately, this causes osteopenia and decreased bone mineral density.
Diagnosis and Differential Diagnosis of Rickets
Patient blood samples indicate decreased calcium and phosphate levels. Alkaline phosphatase, which represents the activity in the bone, is generally high in patients with rickets.
Persons suffering from calciopenic rickets usually have elevated parathyroid hormone; initially, the increase may compensate for decreased calcium levels. Ultimately, serum calcium levels decrease. Also, the urine calcium/urine creatinine ratio should be tested.
Differential diagnosis of rickets
- Achondroplasia and metaphyseal chondrodysplasia characteristically present similarly with bilateral bowed legs. However, inorganic phosphorus and PTH hormone levels are normal, which helps rule out these diseases.
- 1,25 dihydroxy vitamin D forms in the kidney. The kidneys also help maintain calcium homeostasis. In cases of renal insufficiency, there are concomitant bone diseases, characteristically known as renal osteodystrophy. This mimics rickets but can be excluded by assessing patients’ serum creatinine levels (would be elevated).
- Blount disease: Disruption of the proximal tibial physis (growth plate) on the medial aspect. The radiological features are the key to the differential diagnosis.
- Other differential diagnoses include hypophosphatasia (the difference is that there would be a low level of alkaline phosphatase) and transient hyperphosphatemia.
Treatment of Rickets
Since the disease occurs due to deficiency of vitamin D, calcium, and phosphate, supplementation of all three in the diet is main treatment. Also, exposure to sunlight (ultraviolet B) is a treatment for this patient (however, increased exposure may increase the risk of skin cancer). Diet-rich sources of vitamin D are cod liver oil and halibut oil.
In the case of vitamin D deficiency rickets (nutritional rickets), treatment consists of ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3). There are two schools of thought on high dose vs. low dose vitamin D. Vitamin D dosage is generally 5,000 to 10,000 International Units (IU). It should be given until the biochemical values are normal after radiological cure occurs for the patient.
If treatment does not include calcium supplements, then there is an elevation of parathyroid hormone, and it might result in hungry bone syndrome, which is a rapid “rebound” recalcification of the bones after prolonged hypocalcemia. Vitamin D supplements need to be given along with calcium to avoid this.
The recommended dose for infants is 400 IU a day. In Europe, stoss therapy (Single high-dose oral vitamin D3 (stoss) consists of giving 6 lakh international units in a single day for the treatment. The single-day stoss dose should be divided into 4 to 6 doses in the day. The advantages are that there is no issue about compliance (which might be affected in the gradual method). The disadvantage is the increased risk of hypercalcemia. In cases of severe deformity, orthopedic correction is required, especially for the Genu valgum, to straighten the patient’s leg.
Prevention of Rickets
Adequate exposure to sunlight holds the key to the prevention of rickets. The mother needs to have sufficient sources of vitamin D from the diet, as well as sunlight exposure, to avoid congenital defects. A diet rich in vitamin D also needs to be taken regularly for prevention.
The supplementation of vitamin D and the intake of a diet rich in vitamin D is especially important in the growing age group. The amount of vitamin D in human milk is very low, especially when babies weight less than 1.5 kg. These are the infants for whom vitamin D supplements are recommended by the US Endocrine Society Clinical Practice and the European Society for Pediatric Gastroenterology.
One of the other innovative steps in preventing rickets is the fortification of milk and cereals with vitamin D.