Adult-Onset Rickets: Underlying Causes to Rule Out

Adult-Onset Rickets: Underlying Causes to Rule Out

Adult-onset rickets—or more precisely osteomalacia—occurs when bones soften due to defective mineralization. While true “rickets” refers to growing children, adults can present with very similar symptoms. If you’re experiencing unexplained bone pain, muscle weakness or spontaneous fractures, it’s important to understand the possible underlying causes, and to work with your healthcare provider to rule them out.

Clinical Features to Recognize
Adult-onset rickets often presents subtly. Common signs and symptoms include:

• Diffuse bone pain, especially in the hips, legs or lower back
• Muscle weakness, particularly in the shoulders or pelvic girdle
• Difficulty walking or climbing stairs
• Increased risk of fractures, often in ribs, hips or feet
• Waddling gait or bone tenderness when pressed

Because these signs overlap with many other conditions (like osteoporosis or arthritis), targeted testing and a careful review of possible causes are essential.

Key Laboratory Tests and Imaging
To zero in on adult-onset rickets, your doctor will likely order:

• Serum calcium and phosphate
• Alkaline phosphatase (ALP)
• Parathyroid hormone (PTH)
• 25-hydroxyvitamin D (25[OH]D) and sometimes 1,25-dihydroxyvitamin D
• Renal function tests (creatinine, blood urea nitrogen)
• Urinary calcium and phosphate excretion
• X-rays or bone density scans (DEXA)
• In select cases, bone biopsy

Abnormalities such as low phosphate, elevated ALP and low vitamin D point toward osteomalacia. From there, these are the main causes to rule out:

1. Nutritional Vitamin D Deficiency
   Vitamin D is crucial for calcium absorption. Inadequate sun exposure, poor diet or strict vegan/vegetarian diets can lead to deficiency. Risk factors include:

• Living in northern latitudes or wearing full-body coverings
• Dark skin pigmentation (requires more sun for the same vitamin D synthesis)
• Lack of dietary sources (e.g., fatty fish, fortified dairy)

2. Malabsorption Syndromes
   Even with adequate intake, some people cannot absorb fat-soluble vitamins properly. Conditions to consider:

• Celiac disease or inflammatory bowel disease
• Gastric bypass or other bariatric surgeries
• Chronic pancreatitis or cystic fibrosis

3. Chronic Kidney Disease (CKD)
   Healthy kidneys convert 25(OH)D into its active form, 1,25-dihydroxyvitamin D. In CKD:

• Reduced 1-alpha hydroxylase activity
• Secondary hyperparathyroidism (drives phosphate loss)
• Bone demineralization

4. Liver Disease
   The liver is needed to hydroxylate vitamin D into 25(OH)D. Severely impaired liver function (cirrhosis, hepatitis) can lead to substrate deficiency.

5. Tumor-Induced Osteomalacia (TIO)
   Rare mesenchymal tumors produce excess fibroblast growth factor 23 (FGF23), causing phosphate wasting and low vitamin D activation. Clues include:

• Hypophosphatemia that doesn’t respond to supplements
• Persistent bone pain and muscle weakness
• Tumor localization via specialized imaging (e.g., PET/CT)

6. Hereditary or Genetic Disorders
   Although most present in childhood, milder forms can manifest later:

• X-linked hypophosphatemia (XLH)
• Autosomal recessive or dominant hypophosphatemic rickets
• Hypophosphatasia (low alkaline phosphatase activity)

Family history or genetic testing may reveal these rare causes.

7. Fanconi Syndrome
   A proximal renal tubular defect leads to losses of phosphate, glucose, bicarbonate and other substances in the urine. Signs include:

• Polyuria, polydipsia
• Metabolic acidosis
• Hypophosphatemia unresponsive to oral phosphate

8. Hyperparathyroidism
   Primary or secondary overactivity of the parathyroid glands elevates PTH, driving phosphate loss and bone resorption. Look for:

• High PTH with low or normal calcium
• Bone pain, osteoporosis
• Kidney stones (in primary hyperparathyroidism)

9. Medications and Toxins
   Certain drugs and exposures can impair vitamin D metabolism or bone mineralization:

• Anticonvulsants (phenytoin, phenobarbital)
• Antiretrovirals (tenofovir)
• Glucocorticoids (long-term use)
• Heavy metals (cadmium, lead)

10. Nutritional Calcium Deficiency
    Less common than vitamin D deficiency, very low dietary calcium or lactose intolerance can exacerbate bone softening.

How to Narrow Down the Cause
A stepwise approach helps your doctor pinpoint the culprit:

1. Detailed History and Physical Exam

   • Diet, sun exposure, travel history
   • Surgical and medical history (GI surgeries, kidney/liver disease)
   • Family history of bone disorders

2. Laboratory Review

   • Low 25(OH)D suggests nutritional deficiency or malabsorption
   • Low phosphate with elevated FGF23 points to TIO or genetic causes
   • High PTH with low calcium may indicate hyperparathyroidism

3. Imaging Studies

   • X-rays: Looser’s zones (pseudofractures) in osteomalacia
   • DEXA scan: Diffuse reduction in bone density
   • PET/CT or octreotide scan: Localize occult tumors in suspected TIO

4. Specialized Tests (as needed)

   • Genetic panels for hypophosphatemic rickets
   • Renal tubular function tests for Fanconi syndrome
   • Liver biopsy or elastography for severe liver disease

Treatment hinges on correcting the underlying issue:

• Nutritional or sunlight deficiency: vitamin D supplementation (ergocalciferol or cholecalciferol) and moderate sun exposure
• Malabsorption: treat the GI condition, consider higher or intramuscular vitamin D doses
• CKD: active vitamin D analogs (calcitriol), phosphate binders, manage secondary hyperparathyroidism
• TIO: surgical removal of the responsible tumor
• Genetic forms: burosumab (an anti-FGF23 antibody) for X-linked hypophosphatemia, phosphate and vitamin D analogs
• Fanconi syndrome: supportive care, phosphate supplementation, treat underlying cause
• Hyperparathyroidism: parathyroidectomy in primary cases; optimize CKD management in secondary cases
• Medication-induced: reassess need for the offending drug, consider alternatives

When to Seek Help or Further Evaluation
If you have any of the following, it’s important to discuss them with your doctor right away:

• Severe bone pain that limits daily activities
• New, unexplained muscle weakness
• Stress fractures or pseudofractures on imaging
• Lab values showing persistent hypophosphatemia or very low vitamin D despite supplements

You might also consider taking a free, online symptom check, using the doctor approved Ubie Symptom Checker to help identify potential causes and guide your conversation with a healthcare provider.

Final Thoughts
Adult-onset rickets (osteomalacia) can stem from a wide array of conditions. A systematic approach—combining a thorough history, targeted labs, imaging and sometimes genetic testing—helps rule out each potential cause. Treatment is tailored to the root problem, often leading to significant relief and improved bone health.

If you suspect you have adult-onset rickets or are experiencing serious symptoms, please speak to a doctor. Timely evaluation and management can prevent complications and help you get back to your normal activities.