The impact of multiple myeloma on bones: how to prevent bone fractures?

Understanding the impact of multiple myeloma on bone health

Multiple myeloma, also known as plasma cell myeloma or Kahler's disease, is a type of blood cancer that affects certain cells of the immune system: plasma cells (a type of white blood cells that produce antibodies, mainly located in the bone marrow). When they become abnormal, these plasma cells proliferate uncontrollably and disrupt the natural balance of bone renewal, leading to increased skeletal fragility.

The role of abnormal plasmocytes in bone destruction

In a healthy bone, there is a constant balance between bone formation (by osteoblasts) and bone resorption (by osteoclasts). This balance ensures that the skeleton remains strong throughout life.

However, in multiple myeloma:

• Malignant plasma cells produce substances that excessively stimulate the osteoclasts responsible for bone destruction.
  
• At the same time, these same cancer cells inhibit the action of osteoblasts, preventing bone repair and reconstruction.
  
• This imbalance leads to the formation of osteolytic lesions - holes in the bone that make it more fragile and vulnerable to fracture.

Hypercalcaemia and its consequences 

When bones break down rapidly as a result of over-activated osteoclasts, large amounts of calcium are released into the bloodstream, causing hypercalcaemia. This abnormal increase in calcium levels can lead to a number of symptoms:

• Intense fatigue and muscle weakness,
  
• Nausea, vomiting and constipation,
  
• Impaired concentration and mental confusion,
  
• Kidney problems (kidney stones, kidney failure).

Hypercalcaemia, which is common in patients with multiple myeloma, worsens their general condition and may indirectly cause falls and fractures.

Bones are becoming more fragile 

Several mechanisms contribute to bone fragility in multiple myeloma:

• Development of osteolytic lesions: ‘holes’ in the bone weaken its structure, increasing the risk of spontaneous fractures.
  
• Loss of bone density: the reduced activity of osteoblasts prevents bone regeneration.
  
• Reduced mobility: pain and fatigue restrict physical activity, exacerbating the loss of muscle and bone mass.
  
• Side-effects of treatment: certain drugs used to treat myeloma can increase bone demineralisation. 

Most common locations of bone lesions 

Fractures in multiple myeloma occur mainly in areas where osteolytic lesions are most numerous. The parts of the body most affected are:

• The spine: the vertebrae are particularly vulnerable to compression fractures, which can lead to loss of height, chronic pain and sometimes neurological damage (compression of the spinal cord).
  
• The ribs: spontaneous fractures may occur, causing acute chest pain.
  
• The pelvis: pelvic damage can complicate mobility and increase the risk of falls.
  
• The femur and humerus: these long bones can fracture even after a minor impact, especially due to reduced bone density.
  

Some of these fractures may be silent at first, but gradually lead to pain and loss of mobility.

Aggravating factors in patients with multiple myeloma 

Age and comorbidities 

With age, bone density naturally decreases, making older people even more vulnerable to fractures. The majority of patients with multiple myeloma are diagnosed after the age of 60, which accentuates the problem.

Other associated health conditions may also play a role:

• Pre-existing osteoporosis: bone loss prior to the diagnosis of myeloma further exacerbates bone fragility.
  
• Kidney disease: Common in myeloma patients (due to hypercalcaemia), this condition alters the metabolism of calcium and phosphorus, which are essential for bone strength.
  
• Muscular weakness and balance disorders: inactivity and fatigue encourage falls, increasing the risk of fractures.
  
• Nutritional deficiencies: lack of vitamin D and calcium can accelerate bone demineralisation.

Treatments of multiple myeloma

While treatments for multiple myeloma are aimed at slowing the progression of the disease, some of them can also weaken the bones:

• Corticosteroids: often used in combination with other treatments, they accelerate bone resorption and can cause osteoporosis.
  
• Chemotherapy: can alter bone metabolism and reduce the production of osteoblasts, preventing bone reconstruction.
  
• Targeted therapies and immunomodulators: can cause side effects such as fatigue and muscle weakness, increasing the risk of falls.
  
• Inactivity linked to side effects: pain and fatigue often reduce mobility, leading to muscle loss and reduced bone strength.

How to prevent bone fractures in patients with multiple myeloma 

The prevention of fractures in patients with multiple myeloma is based on several complementary strategies. It involves both medication and lifestyle adjustments.

Drug treatments 

One of the major prevention tools is specific medication, that helps strengthen bones and limit their deterioration.
Bisphosphonates (zoledronic acid, pamidronate) act by inhibiting the action of osteoclasts, cells responsible for excessive bone resorption. Their effect is to:

• Slow down bone degradation,
  
• Reduce the risk of vertebral and long bone fractures,
  
• Reduce bone pain associated with myeloma lesions.
  

Bisphosphonates are generally administered by infusion once a month. However, they can have side effects such as muscle pain, digestive problems and a risk of osteonecrosis of the jaw, which is rare but serious.

Exercising

Physical exercise plays an essential role in maintaining strong bones and muscles. Even in the presence of pain, moderate and appropriate activity can help, as it:

• strengthens muscles and improves balance, thereby reducing the risk of falling,
  
• preserves bone density by stimulating bone regeneration,
  
• reduces fatigue and improves quality of life.

Diet and supplements to improve bone health 

Diet plays a key role in preventing bone fragility. An adequate intake of calcium, vitamin D and protein is essential.

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