Osteomalacia and Rickets

Essentials of Diagnosis

General Considerations

Osteomalacia is the adult form of rickets. It is a condition resulting from a calcium and phosphorus deficiency in the bone. It may be caused by insufficient absorption from the intestine, due either to a lack of calcium alone, or a lack of or resistance to the action of vitamin D. In adults, this form of osteomalacia is almost always found in association with disorders of fat absorption (diarrhea, sprue, panereatitis, gastrectomy). The other more common variety of osteomalacia is found in association with renal calcium or phosphorus losses ("vitamin D-resistant rickets"). This is often a familial disorder. It is found in tubular disorders, either tubular "leaks" of phosphate and calcium due to failure of reabsorption, or due to excessive losses asstmated, with tubular acidosis (calcium dissolved out of the bone to spare sodium or potassium, or both). There may be associated glycosuria and aminoaciduria (Fanconi's syndrome). Cases of osteomalacia have been described that are due to chronic phosphate depletion from prolonged use of aluminum hydroxide gels and that occur due to long-term anticonvulsant therapy. A rare case of vitamin D-resistant rickets may be due to a mesenchymal tumor.

Almost all forms of osteomalacia are associated with compensatory, secondary hyperparathyroidism, set off by the low calcium level. It is for this reason that most patients will show only slightly low serum calcium levels (compensated osteomalacia). In chronic uremic states a mixed picture of osteomalacia and secondary hyperparathyroidism is seen ("renal osteodystrophy"). Resistance to the action of vitamin D due to failure of its conversion to the biologically active forms, 25-hydroxycholecalciferol, and 1-25 dihydroxy-cholecalciferol by the liver and kidney, respectively, has recently been demonstrated.

A special form of osteomalacia is the so-called Milkman's syndrome, an x-ray diagnosis of multiple, bilaterally symmetric pseudofractures which may rep-resent the shadows of calluses near arterial blood ves-sels traversing and eroding the soft skeleton. Rickets, which is the counterpart of osteomalacia in the growing child, shows additional features, especially around the epiphyses, which are widened and "motheaten" on x-ray. There is also beading of the ribs, Harrison's groove, bowlegs, and disturbances in growth.

In contrast to osteoporosis, where fractures are more common, osteomalacia is more often associated with bowing of bones.

Clinical Findings

A. Symptoms and Signs :

Manifestations are var-iable, ranging from almost none in mild cases to marked muscular weakness and listlessness in advanced cases. There is usually mild aching of the bones, especially of long bones and ribs, and a tendency to bowing. In the very early and acute osteomalacias a rapidly falling calcium level may be associated with clinical tetany, although this is rare. As compensation takes place, tetanic features are absent. In states of deficient absorption, other features of the sprue syndrome, such as glossy tongue or anemia, may be present. A low potassium syndrome with muscular weakness and paralysis may be present with renal tubular disorders.

B. Laboratory Findings :

Serum calcium is low or normal, but never high. Serum phosphate is low (may be normal in early stages). The alkaline phosphatase is elevated except in the early phase. Urinary calcium and phosphate are usually low in absorption disorders and high in renal lesions. The intravenous calcium infusion test demonstrates avidity of bone for calcium (80-90 per cent retained) in osteomalacia due to malabsorption. Laboratory findings of the primary steatorrhea or renal disease may be present. In renal tubular acidosis the serum + is low and the serum chloride level is elevated; the serum potassium may be very low; the urinary pH is fixed near the alkaline side. Glycosuria and aminoaciduria are found in the Fanconi syndrome.

C. X-Ray Findings :

Involvement of the pelvis and long bones, with demineralization and bowing; less of-ten, the spine and skull are involved as well. Fractures are rare except for "pseudo fractures."

Differential Diagnosis

It is most important to recognize osteomalacia and consider it in the differential diagnosis of bone disease since it is a potentially curable disease. The childhood forms may be mistaken for osteogenesis imperfecta or other nonmetabolic bone disorders.

The acute forms must be differentiated from other forms of tetany. The long-standing disease enters into the differential diagnosis of any metabolic or generalized nonmetabolic bone disease. The pseudofracture is often the only outstanding sign of latent osteomalacia. Osteoporosis may exist as well, and may obscure the osteomalacia. At times the diag-nosis is confirmed by a rise and subsequent fall of the serum alkaline phosphatase after treatment with vita-min D and calcium. Renal tubular acidosis is a cause of nephrocalcinosis, and must be considered in the differential diagnosis of kidney calcifications with bone disease, such as hyperparathyroidism. The joint aches and pains may be mistaken for some form of arthritis. The cachexia suggests malignancy. Bone biopsy (eg, of the rib) with tetracycline labeling or microradiography may establish the diagnosis of latent osteomalacia.

Treatment

A. Specific Measures:

  1. Rickets- Vitamin D, even in small doses, is spe-cific; 2000-5000 units daily are adequate unless resist-ance to vitamin D is present.
  2. Adult osteomalacia and renal rickets- Vitamin D is specific, but very large doses are necessary to over-come the resistance to its calcium absorptive action and to prevent renal loss of phosphate. Give until an effect is noted on the blood calcium. The usual dose is 25-100 thousand units daily. Doses up to 300,000 units or more daily may be necessary, but if the doses are over 100,000 daily, they must be used cautiously with periodic determination of serum and urine calcium; the serum phosphate may remain low.
  3. Pancreatic insufficiency- Adequate replacement therapy with pancreatic enzyme is of paramount importance; high calcium intake and vitamin K are also of value.
  4. Sprue syndrome- Folic acid and vitamin B r2 appear to be of value. A gluten-free diet should be used in patients with gluten sensitivity.
  5. Some rare forms of renal disease- Treatment is aimed at the altered renal physiology, eg, alkali therapy and potassium replacement in renal tubular acido-sis, phosphate therapy, etc.

B. General Measures :

High-calcium diet and calcium gluconate or calcium lactate, 4-20 gm daily, or calcium carbonate, 4-8 gm daily. A high-phosphate diet or phosphate salts may be of value in certain types of renal rickets.

C. Vitamin D Metabolites :

In the future, the increasing availability of the biologically active metabolites of calciferol, 25-hydroxycholecalciferol and 1-25 dihydroxycholecalciferol, will help in the treatment of osteomalacia resistant to vitamin D (eg, chronic liver disease and renal failure).

Prognosis

The prognosis is usually excellent in the absorptive disorders if diagnosed early. This does not hold for certain of the vitamin D-resistant forms of osteomalacia or rickets or for Fanconi's disease, which respond slowly or not at all unless huge amounts of vitamin D are given.

Hypercalcemia may occur as a complication of therapy. In severely refractory cases, parathy-roidectomy has improved the prognosis. In the renal forms, the ultimate prognosis is that of the basic kidney disease. Respiratory paralysis due to hypokalemia may prove fatal.

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