Osteomalacia (patient information)

Patient information

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Ibrahim Elkhayat, M.B.B.Ch.[2]

Osteomalacia is a disorder in which the newly formed and remodeled bone matrix (osteoid) does not become properly mineralized, causing bones to become softer than normal. It is different from osteoporosis, in which bone mass is reduced. Osteomalacia can cause bone pain, muscle weakness, fractures, and difficulty walking. When caused by nutritional deficiency, osteomalacia is often treatable and the mineralization defect can improve with appropriate treatment.

What causes osteomalacia?

The cause is important because treatment depends on the underlying problem. Causes include:

• Vitamin D deficiency.
• Inadequate dietary calcium. Low dietary calcium on its own can be an important cause of osteomalacia, particularly in populations with low calcium intake.
• Conditions that reduce absorption of nutrients, including gastrointestinal disease and some bariatric procedures.
• Kidney or liver disease that interferes with normal vitamin D and mineral metabolism.
• Medicines that interfere with vitamin D metabolism.
• Disorders that cause excessive loss of phosphate through the kidneys.
• Hereditary disorders such as X-linked hypophosphatemia.
• Tumor-induced osteomalacia, a rare disorder caused by inappropriate phosphate wasting.

Who is at higher risk?

Risk is increased in people with:

• Darker skin pigmentation.
• Limited exposure to sunlight or extensive covering of the skin.
• Older age, particularly in people who are housebound or institutionalized.
• Pregnancy or breastfeeding.
• Poor dietary calcium or vitamin D intake.
• Conditions or surgery that reduce absorption of nutrients.

What symptoms can it cause?

Common symptoms and findings include:

• Diffuse or persistent bone pain and tenderness.
• Muscle weakness, particularly weakness around the hips and shoulders.
• Difficulty climbing stairs, rising from a chair, or walking.
• Fatigue.
• Fractures or pseudofractures in more advanced disease.

The symptoms may be nonspecific, and osteomalacia can therefore be mistaken for osteoporosis, rheumatologic disease, or a neuromuscular disorder.

How is osteomalacia diagnosed?

Diagnosis usually combines the clinical picture with blood and urine tests and, when appropriate, imaging.

Blood tests may include:

• 25-hydroxyvitamin D (25-OHD).
• Calcium.
• Phosphate.
• Alkaline phosphatase (ALP).
• Parathyroid hormone (PTH).
• Additional tests directed at the suspected cause.

A DXA scan measures bone mineral density but does not by itself diagnose or exclude osteomalacia. Osteomalacia may occur with a low bone mineral density and can therefore be mistaken for osteoporosis.

Looser zones (pseudofractures) are a characteristic radiographic finding in severe osteomalacia, but they are not present in every patient.

How is osteomalacia treated?

Treatment depends on the underlying cause.

For nutritional osteomalacia, treatment generally involves vitamin D replacement together with adequate calcium intake. Initial replacement is followed by maintenance supplementation. Maintenance treatment may need to continue long term, particularly when the underlying risk factor persists.

If osteomalacia is caused by malabsorption or another underlying disease, that condition also needs to be treated.

Kidney or liver disease can interfere with the body's ability to activate vitamin D. Some patients with these conditions therefore require an activated form of vitamin D, such as alfacalcidol or calcitriol, rather than ordinary vitamin D. Patients should not substitute or adjust vitamin D preparations on their own.

Patients with phosphate-wasting, hereditary, or tumor-induced osteomalacia may require specialist treatment. Depending on the disorder, treatment may include phosphate with active vitamin D, burosumab for selected phosphate-wasting disorders such as X-linked hypophosphatemia or tumor-induced osteomalacia, or treatment of the causative tumor.

What should patients know about treatment and recovery?

Improvement in bone pain, muscle weakness, and biochemical abnormalities generally occurs over the first few months of appropriate treatment, but complete skeletal remineralization and recovery of bone strength can take longer.

Blood tests are used to assess the response to treatment and to monitor calcium, phosphate, vitamin D, and other relevant biochemical measures.

Blood calcium can sometimes fall when severe nutritional deficiency is treated. This is one reason calcium may be given together with vitamin D and why blood tests are checked during treatment. Patients should promptly contact their healthcare team if they develop new muscle cramps, tingling around the mouth or in the hands, or other symptoms suggestive of significant low calcium.

Patients should not stop maintenance treatment simply because their symptoms have improved. Recurrence can occur when maintenance supplementation is stopped or when an underlying problem, such as malabsorption, remains untreated.

When should a patient seek medical attention?

Patients with persistent or worsening bone pain, new weakness, difficulty walking, or suspected fractures should contact their healthcare provider.

During treatment, new or severe muscle cramps, tingling around the mouth or in the hands, seizures, or other symptoms concerning for significant abnormalities in blood calcium require prompt medical assessment.

Important points to remember

• Osteomalacia is not the same as osteoporosis.
• A low or normal DXA result does not by itself establish or exclude osteomalacia.
• The underlying cause should be identified whenever possible.
• Vitamin D and calcium treatment should be taken as prescribed and followed by appropriate monitoring.
• Patients with unexplained low phosphate or renal phosphate wasting may need evaluation for a phosphate-wasting disorder or tumor-induced osteomalacia.
• Some patients with kidney or liver disease require activated vitamin D rather than ordinary vitamin D supplements.
• Do not change vitamin D, calcium, or phosphate treatment without discussing it with the treating clinician.