Table of Contents
Definition and Epidemiology of Rickets
According to the standard textbooks, rickets are defined as the imperfection, distortion and softening of the bones due to deficiency of vitamin D. Vitamin D is basically a fat soluble vitamin and the forms of the essential vitamin in the body.
As rickets is mainly caused by the deficiency of vitamin D, and Vitamin D is a hormone which is synthesized on exposure to sunlight, the epidemiology of rickets mainly consists of those regions where exposure to sunlight is reduced. The increase in the growth spurt especially in the puberty is one of the reasons for the manifestation of rickets.
The regions where the diet consist of inadequate vitamin D and calcium also are linked to the development of rickets.
Though rickets is rare in the developed countries, it forms one of the most frequent diseases of children in developing countries. The poverty and inadequate availability of food are also reasons for development of rickets in children.
Etiology and Classification of Rickets
Vitamin D is a fat soluble hormone responsible for maintaining the serum phosphate and calcium level which in turn is of foremost importance for the mineralisation of the bone. The exposure to sunlight causes the conversion of vitamin D from its inactive to the active form in the cells of the skin.
The primary reason for congenital rickets is the deficiency of vitamin D in the mother. The vitamin D is transferred in the form of 25 hydroxyvitamin D from the mother to the fetus as this form crosses the placenta.
Some of the risk factors for the development of vitamin D deficiency in the newborn infant are:
Deficiency of vitamin D in the mother during the pregnancy
Exclusive prolonged breastfeeding without any vitamin D supplementation
Dark skin complexion
Very low sun exposure.
In addition to this, other gastroenterological intervention and disease of the intestine also hamper the normal absorption of vitamin D from the nutritional supplement.
The reason for rickets in children are mainly due to the deficiency of vitamin D. Vitamin D is synthesised by the exposure to the sunlight. The insufficient exposure to sunlight and certain dietary habits like exclusive cereal based diet are biological reasons for the development of rickets in children.
In some cases though, there may be a normal level of vitamin D but there occurs decrease in the activity of the vitamin D basically due to the lack of conversion to the active metabolite and the resistance of the receptor to the metabolite. This results in what is known as calciopenic rickets.
There is also a genetic cause for rickets and it is known as vitamin D Resistant Rickets (X- linked hypophosphatemia). It is also known that it can also occur because of phosphate deficiency, which has been reported as the cause for 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 1-alpha-hydroxylase enzyme
- Type 2: mutation in the calcitriol receptor
- Hypocalcemia-related rickets
- Hypophosphatemia-related rickets
- Congenital hyperphosphatemia
- Autosomal dominant hypophosphatemic rickets
- Autosomal recessive hypophosphatemic rickets
- Vitamin D-resistant rickets
- Secondary to malabsorption
- Fanconi syndrome
- Congenital hyperphosphatemia
- Rickets secondary to other diseases
- In addition to this, the 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 the deficiency of calcium, though there occurs proliferation of the chondrocytes as well as its hypertrophy, the concurrent invasion by the vascular tissue and the conversion of the formed chondrocytes to the mineralized structure is deficient.
This results in a disorganised growth plate and expansion of the proliferative zone. Ultimately, the stability of the bone is severely compromised leading to bowing and other characteristic features of rickets.
The symptoms are very characteristic in children.
- The fontanelles are present at the junction of the skull bones and in the case of rickets, there occurs delay in the time of closure of fontanelles. As there occcurs defect in mineralisation of the skull bones, there is bossing due to the pressure by the underlying brain and this is especially prominent in the parietal and frontal regions.
- Both Genu varum as well as Genu valgum can occur based on the age at which the rickets manifest. In case of the the rickets in toddlers, Genu Varum occurs, whereas in older children, Genu valgum occurs.
- Deformity in the spine (kyphoscoliosis) and increase in the risk of tetany
- The skull bones are soft and this is 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 get broadened especially the upper arm bones (radius and ulna) and the lower arm bones (tibia).
- Proliferation of the chondrocytes in the rickets manifest as the enlargement of the costochondral junction which forms characteristic beading along the chest known as rachitic rosary and there also occurs widening of the wrist.
- There occurs tenderness of the bones, problem in the dental architecture, greenstick fracture and increased weakness of the muscle. The growth of the child gets affected and disturbed.
Progression and Complications of Rickets
The progression of rickets leads to the bowing of both the legs with the development of Genu valgum. The growth also severely gets hampered due to the occurrence of rickets in the younger age group. Genu valgum is characteristic known as the knock knees in which the straightening of the leg leads to the touching of both the legs to one another and the knees are basically angled in.
The severe hampering of the growth of the child happens on the occurrence of rickets in the younger group. This results in the development of short stature. The rickets on the long run also lead to the development of osteoarthritis and other degenerative disorders of the bone. Ultimate read, this results in osteopenia and decrease in the bone mineral density.
Diagnosis and Differential Diagnosis of Rickets
A decrease in the level of calcium and phosphate is seen in the blood of the patient. Alkaline phosphatase, which represents the activity in the bone, is generally high in the patients of rickets.
The persons suffering from calciopenic rickets usually have elevated parathyroid hormone and this increase might initially compensate for the decrease of the calcium level. But ultimately, the decrease in the serum calcium levels occur. In addition to this, there also occurs a need for talking monitoring of the urine calcium level in relation to the creatinine level.
Differential diagnosis of rickets
- Achondroplasia and metaphyseal chondrodysplasia characteristically presents similarly with bilateral bowed legs but it should be noted that the inorganic phosphorus and the PTH hormone level would be normal and these would help in the exclusion of these diseases.
- Renal osteodystrophy: It is well known that the kidney is an important organ where the formation of 1,25 dihydroxy vitamin D occurs. In addition to this, the kidneys also play a central role in maintaining the milieu of the calcium. So in case of renal insufficiency, there occur concomitant bone diseases characteristically known as renal osteodystrophy. This mimics rickets but can be excluded by means of taking into consideration the serum creatinine of the patients (would be elevated).
- Blount disease: Disruption of the proximal tibialphysis on the medial aspect. The radiological features form the key in differentiating.
- Other differential diagnosis include hypophosphatasia (the difference is that there would be low level of alkaline phosphatase), transient hyperphosphatemia.
Treatment of Rickets
As the disease occurs due to the deficiency of vitamin D, calcium and phosphate, the supplementation of all the three in the diet forms the main part of the treatment. In addition to this, the exposure to sunlight (ultraviolet B) is a treatment for this patient (there is another school of thought of recommendation of supplementation instead of the exposure, as increased exposure increases the risk of skin cancer). The diet rich sources of vitamin D are cod liver oil and halibut oil.
In the cases of vitamin D deficiency rickets (nutritional rickets), the treatment consists of ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3). There are two schools of thoughts on starting the high dose vitamin D or the low dose vitamin D. Vitamin D is generally given 5,000 to 10,000 International Units (IU) and is to be given until the biochemical as soon as radiological cure occurs for the patient.
If the calcium supplements are not present in the treatment, then there is an elevation of parathyroid hormone and it might result in a syndrome known as hungry bone syndrome. So in order to avoid this, the vitamin D supplement needs to be given along with calcium.
The recommended dose for infants is 400 IU a day. The stoss therapy is basically giving 6 lakh international units a single day for the treatment. The single day stoss dose should be divided into 4 to 6 doses in the day. The advantages is that there is no issue for the compliance (which might be affected in the gradual method). The disadvantages of this therapy is the increased risk of hypercalcemia.
In the case of severe deformity, the orthopaedic correction is required for the deformities. This is especially required for the Genu valgum. The reconstruction surgery is done to straighten the leg of the patient.
Prevention of Rickets
Adequate exposure to sunlight holds the key in prevention of rickets. In order to avoid congenital defects, the mother needs to have sufficient sources of vitamin D from the diet as well as on exposure to the sunlight. A diet rich in vitamin D also needs to be taken regularly for the prevention.
The supplementation of vitamin D and the intake of the diet rich in vitamin D is especially required in the growing age group of the puberty. In case of children who are exclusively breastfed, the amount of vitamin D present in the human milk is very low, especially with the babies with a weight of less than 1.5 kg. These are the infants in whom the vitamin D supplements are recommended and the recommendations are given by the US Endocrine Society Clinical Practice and the European Society for Paediatric Gastroenterology.
One of the other innovative steps in preventing the occurrence of rickets especially the nutrition details is the fortification of the milk cereals with vitamin D.