Rickets (Greek Rhachis, spine), is a disease of the growing bone with disturbed mineralization of the bones and disorganization of the growth joints in children. It is caused by a disturbance of the calcium-phosphate metabolism, which is usually caused by a too low intake or a metabolic disorder. In adulthood, rickets is referred to as osteomalacia.
Rickets is not a notifiable disease and is therefore difficult to quantify. Statistically, however, it is noticeable that especially African-American children are affected more often than others. The occurrence of the typical symptoms, however, is very rare.
Most children only show a laboratory chemical vitamin D deficiency. This is very common and also found in highly developed countries. An American study showed that almost half of all girls had a significantly low vitamin D level in their blood at the end of winter.
In addition, in countries with high sun exposure the Vitamin D deficiency occurs epidemiologically, since the women in these countries are often strongly veiled for religious reasons. In European countries, especially infants and children who receive a macrobiotic diet show symptoms of rickets. The balance between calcium and phosphate in the body is regulated by the hormones calcitriol (vitamin D), parathormone and calcitonin.
The concentration of the two substances is closely linked and is precisely regulated. The largest amount of calcium and phosphate is stored in the bones in the form of hydroxyapatite. If the body registers too much or too little phosphate or calcium, parathormone is released.
This releases calcium from the bones or builds it into the bones. Excess phosphate is excreted via the kidneys, or, in the case of phosphate deficiency, it is increasingly reabsorbed from the urine. Calcium can only be absorbed with the help of vitamin D3, which is produced in the skin with the aid of ultraviolet radiation from sunlight.
The vitamin D3 is then converted in the liver and kidneys via various precursors (25-hydroxy-cholecalciferol) to the actually effective calcitriol (1,25-dihydroxy-cholecalciferol) and enables the absorption of calcium into the bones. If vitamin D3 is missing, the bone becomes increasingly brittle as mineralization cannot take place and the typical symptoms of rickets occur. Basically two forms of rickets are distinguished: The more frequent form is the calium deficiency rickets.
This is caused by a lack of vitamin D. This is usually caused by a combination of too little vitamin D intake from food and too little exposure to sunlight. In rare cases, an enzyme defect is responsible for the vitamin D deficiency. This is known as vitamin D-dependent rickets type 1 and type 2.
Furthermore, other intestinal diseases can prevent sufficient vitamin D absorption from the intestines (celiac disease, cystic fibrosis). Certain drugs such as phenytoin and phenobarbital for epilepsy therapy also reduce intestinal absorption and increase the breakdown of vitamin D3. The rarer phosphate deficiency rickets leads to an increased loss of phosphate via the kidneys and thus disturbs the metabolism and hormone regulation in the body.
Phophate diabetes is a congenital form of phosphate loss and is known as familial hypophosphatemic rickets. Other diseases can damage the renal tubules, causing excessive phosphate loss. An exception to these diseases is relative phosphate deficiency in premature babies.
In this case, there may be too much catch-up growth in relation to the low phosphate supply. Already in the second to third month of life the first symptoms of rickets appear. The children suffer from increased jitteriness, restlessness, sweating heavily and develop an itchy skin rash (miliaria) as a result.
From around 4 months of age, children develop a frog belly, suffer from constipation and the first softening of the bones of the skull (craniotabes). In addition, the calcium deficiency leads to hyperexcitability of the musculature up to muscle cramps. The skull becomes increasingly flattened and the expansion of the bone sutures results in the shape of a square skull within another month.
The wrists and ankles also become increasingly wider (Marfan’s sign). At the growth joints of the ribs of the ribcage, pearl-like distensions appear, which are called rosary.On average, teeth erupt later and show enamel defects. Since the thorax is unusually soft, the muscle pull of the diaphragm leads to retractions (Harrison’s furrow).
Furthermore, leg curvatures, especially bow legs, occur. These typical signs are only found in childhood. In the case of a newly acquired rickets in adulthood, known as osteomalacia, no typical bone deformations occur.
Here, dull bone pain and pathological fractures are typically found. Typical signs of rickets include restlessness, sweating and a sweat-induced rash, as well as increased startledness, already in the first three months of life. In the course of the disease, the onset of muscle weakness leads to a conspicuously distended abdomen (frog belly), which is caused by the flaccidity of the abdominal muscles, flatulence and tendency to constipation.
In addition, there are first signs of bone softening (craniotabes), which leads to a flattening of the back of the head and, in the course of time, to an increased spreading of the skull sutures with the formation of a square skull. Muscular hyperexcitability and a tendency to cramps can be added due to the calcium deficiency. Like the sutures in the skull, the bone-cartilage boundaries of the growth joints also drift up from the ribs (rosary), resulting in widening deformation of the wrists and ankles.
Another sign of bone deformations is the curvature of the legs (bow legs), also the tooth breakthrough can be delayed and the enamel can be defective. The diagnosis is made by the typical bone changes in the x-ray image. However, since it is not possible to differentiate between calcium deficiency rickets and phosphate deficiency rickets, the parathormone must be determined.
This is elevated in the case of calcium deficiency and in the normal range in the case of phosphate deficiency. Furthermore, the individual precursors of vitamin D are determined in the laboratory. Thus it can be determined whether a classic vitamin D deficiency rickets or a vitamin D-dependent form of rickets is present.
In order to be able to diagnose rickets, the patient’s medical history and clinical examination, the typical laboratory findings (elevation of alkaline phosphatase and parathyroid hormone, low vitamin D level) and radiological imaging are also included. Since a general lack of calcium in the bones and a widening of the growth joints as well as joint and bone deformations are typical signs of rickets, these can best be confirmed by conventional x-rays of the wrist (especially in vitamin D deficiency rickets) or knee joint (especially in phosphate deficiency rickets). The bone ends (epiphyses) appear widened in the X-ray, the bone shafts (diaphyses) are low in calcium and have pseudofractures and resorption zones.
The transition zones of bone end and bone shaft (metaphyses) also show widening and appear blurredly limited. The spongy bone ball system of the bones (substantia spongiosa) appears increasingly porous. The therapy is basically based on the form of the rickets.
Children with a classical vitamin D deficiency rickets receive vitamin D and calcium in high doses for 3 weeks. Then the dosage is significantly reduced for the next 3 weeks. After that, it is usually sufficient to change to a calcium-rich diet and sufficient sun exposure.
If vitamin D-dependent rickets type 1 is present, this is not sufficient. In this case the conversion of the precursors is disturbed so that calcitriol must be given in addition to high-dose calcium so that the calcium can be incorporated into the bone. If the bone is refilled with calcium, a lifelong therapy with Calcitriol is sufficient to keep the calcium level in the body.
The therapy of vitamin D-dependent rickets type 2 is much more difficult. Here the oral supply of calcium and the missing vitamin D precursor (dihydroxy cholecalciferol) is often insufficient. Therefore, at the beginning of the therapy, calcium must often be supplied in high doses via an infusion.
If the body is then saturated with sufficient calcium, calcium must continue to be ingested orally in very high doses throughout life in order to maintain the calcium level. In the case of phosphate deficiency rickets, phosphate must be given in addition to calcitriol. If the cause of the phosphate deficiency is a congenital enzyme disorder, the substitution is lifelong.
In the case of a kidney disorder, it must be given priority treatment, if possible, in order to restore the body’s own phosphate absorption.The bone deformations usually heal without further therapy, provided that enough calcium and vitamin D is supplied. In the case of severe deformities or phosphate deficiency rickets, surgery is often necessary to restore the correct bone position (repositioning osteotomy). If the rickets are recognized in time and the therapy is initiated early with a diagnosis, most bone malpositions and deformations regress, but the underlying disease or the hormonal dysregulation behind the disease cannot be completely cured. However, the symptoms of rickets can still be contained by temporary or even lifelong vitamin D or calcitriol substitution, possible phosphate substitution and subsequent prophylaxis in the form of sufficient calcium-containing food intake and exposure to sunlight. In the most severe cases of rickets, however, the deformations of the legs (bow legs) can still remain, so that splinting with orthoses or even a conversion osteosynthesis may be necessary in the course of therapy.
