Kidney Disease And Bone Disorders
Contrary to popular belief, bones are far from a mere scaffolding made of calcium and phosphorus to support the tissues and organs of the human body. The bone is a living, dynamic tissue which is constantly being rebuilt, broken down and remodeled. All this activity takes place mainly under the control of the kidneys and the parathyroid glands, which are four small glands placed in the neck in close relation to the thyroid gland.
High levels of parathyroid hormone leads to an interesting constellation of symptoms described as bones, stones, groans and moans. These manifest as multiple fractures of bones, multiple kidney stones, abdominal pain which makes the patient groan and psychological problems which make the patient moan!
The kidneys control bone activity by maintaining optimal levels of calcium and phosphorus. This it does either, directly by synthesising the active form of vitamin D or indirectly by influencing the parathyroid glands.
The sole function of the parathyroid glands is to produce parathyroid hormone (PTH).
PTH maintains blood calcium levels (by leaching it from the bones in times of crisis) and maintains blood phosphorus levels (by stimulating the kidneys to excrete it).
When the kidneys are not functioning properly, the blood calcium levels drop as the active form of vitamin D (called calcitriol) is not produced. Calcitriol is responsible for absorbing dietary calcium from the gut as well as reclaiming calcium from the urine. Also, kidney disease results in impaired excretion of phosphorus in the urine leading to high blood phosphorus levels.
The low calcium and high phosphorus levels finally lead to hyper-functioning of the parathyroid glands and overproduction of PTHP which removes calcium from the bones leading to brittle and weak bones. The bone disorder due to kidney disease is often silent and without symptoms, hence it is called a ‘silent crippler.’
Bone disorders due to kidney disease only happen in chronic kidney disease, which means kidney dysfunction which has been present since at least three months. Those with kidney disease of short duration, also called acute kidney disease, never get bone disorders.
Bone disorders due to kidney disease are most serious in children as their bones are still growing. These children have slower bone growth and thus short stature. Many develop deformities of limbs which are commonly known as ‘renal rickets,’ The other form of rickets is ‘vitamin D deficiency rickets.’
The kidneys control bone activity by maintaining optimal levels of calcium and phosphorus. This it does either, directly by synthesising the active form of vitamin D or indirectly by influencing the parathyroid glands
- Adults with kidney associated bone disease develop joint and bone pains and frequent fractures.
- High amounts of phosphorus bind with free calcium in the blood and form calcium phosphate. This gets deposited in the blood vessels causing narrowing and compromised blood supply to vital organs like the brain and the heart leading to brain strokes and heart attacks.
- Also, deposition of calcium phosphate in the blood vessels of the limbs can cause gangrene and limb loss.
- Would you, in your wildest dreams, have imagined that bone disease can lead to stroke, heart attack and gangrene?
- Bone disorders due to kidney disease can be diagnosed by checking blood levels of calcium. phosphorus, PTH (Parathyroid hormone) and vitamin D.
- Classically, calcium and vitamin D levels are low and PTH and phosphorus levels are high.
- X-rays and bone scans are also helpful.
- In complicated cases, bone biopsies are performed by removing a small piece of the hip bone and studying them microscopically.
Treatment (Diet Drugs & Dialysis)
Treatment of kidney related bone disease is three-dimensional or 3-D: diet, drugs and dialysis. Reduction of dietary phosphorus is one of the cornerstones of prevention and treatment of bone disease.
Phosphorus is found in almost all foods but is especially high in milk, cheese, peas, beans, nuts, cocoa. aerated drinks and beer. Colas have high phosphorus content which leach calcium from the bones of even healthy individuals making them weak and osteoporotic – so kiss your koala but kick your cola!
These are targeted towards binding phosphorus in the gut to minimise the absorption in to the blood. These may be calcium or non-calcium containing phosphate binders. Various synthetic forms of vitamin D are also prescribed. Certain medications lower parathyroid hormone levels and these are often used.
This is the most efficient way of removing phosphorus from the blood and replacing calcium. However, this is only to be used as a last resort, when all other conservative’ methods have failed. If the PTH levels cannot be controlled medically, the parathyroid glands can be removed surgically.
The kidneys play a crucial role in maintaining bone health and bone integrity. Also, kidney disease often leads to bone disorders. If this is not discovered early and treated aggressively, patients can develop pain, deformities and even become crippled.