Osteolysis is the destruction of bone tissue. It is a normal physiological phenomenon which, compensated by the formation of new tissues, contributes to the continuous regeneration of the skeleton. But, if the balance between the two processes is no longer properly regulated, bone loss can dominate: osteolysis becomes pathological.

It doesn’t look like it, but bone is living tissue. It is constantly being renewed to remain solid. Two types of cells are involved in this remodeling work: 

• osteoclasts, which remove used tissue;
• osteoblasts, which produce new ones to replace them. 

Normally, their respective activities, destruction and construction, are perfectly balanced so that the volume and density of the bone do not move.

This balance is regulated by hormones (estrogen and parathyroid hormone, in particular) and by substances produced by cells of the immune system (cytokines). But, sometimes, this control system breaks down: osteolysis accelerates, to the point of not being able to be sufficiently compensated, and leads to a loss of bone density. We talk about pathological osteolysis.

The causes of pathological osteolysis can be:

• aging : in women in particular, menopause is accompanied by an estrogen deficit. However, these hormones help to slow down the degradation of bone tissue and promote the formation of young bones. Without them, destruction accelerates without being sufficiently compensated. It’s osteoporosis. Even if they are two to three times less affected, men also can be concerned, especially if they have an excessive consumption of alcohol and tobacco, because these two substances impair the regenerative capacities of the tissues;
• endocrine disease : hyperparathyroidism, for example, is an overactivity of the parathyroid glands. These overproduce parathyroid hormone, a hormone that usually stimulates osteolysis in calcium deficiency, in order to release it into the blood. In excess, the molecule causes a runaway in bone destruction;
• multiple myeloma: cancer that forms in the bone marrow and is characterized by an uncontrolled overgrowth of B lymphocytes, a type of white blood cell. The latter then produce excess cytokine, at the very heart of the bone, which activates the osteoclasts responsible for osteolysis;
• bone cancer : an osteolytic-type bone tumor, or bone metastases from another cancer;
• wear around a prosthesis : the contact surface between the bone and the prosthesis can wear out due to stress, causing the formation and accumulation of bone debris which can trigger inflammation which will stimulate osteolysis around the implant. The prosthesis then becomes unstable and needs to be replaced;
• wear and tear or poor blood circulation : erosion of the bony ends of the hand or foot, also called acro-osteolysis, affects the phalanges of the fingers and toes to the point of gradually shortening them, or even making them disappear. This pathology is caused by repetitive inflammation. It can be encountered in particular after repetitive stress exerted on the fingertips (in certain guitarists for example, or after prolonged exposure to vinyl chloride), but also in Raynaud’s syndrome (circulation disorder), scleroderma (disease autoimmune), rheumatoid arthritis (autoimmune inflammatory disease) or some rare hereditary conditions. In some athletes practicing bodybuilding or a contact sport, but also in certain manual trades, bone wear can also be observed in the clavicle.
• Paget’s disease: a benign bone disease, of slow progression, which is characterized by an anarchic bone remodeling in the skull, pelvis, vertebrae, femurs or shins. The bone can hypertrophy in places, weaken in others;
• bone infection, which occurred following a fracture, bone surgery or the fitting of a prosthesis. Bacteria grow in the bone or around the implant, causing inflammation which leads to the destruction of the bone;
• certain drug treatments in the long term, against breast or prostate cancer for example, or based on corticosteroids.

Bone loss, if it is not compensated by the creation of new bone tissue, leads to a loss of density and architectural weakening in the skeleton, which then becomes more often prone to fractures.

At first, especially if it is diffuse like osteoporosis, the loss of bone density is silent. This is why screening is often offered to people at risk (postmenopausal women, etc.). A measurement of bone density (BMD) or bone densitometry then makes it possible to assess the situation and, if necessary, to propose treatment.

When bone loss is more advanced, micro-fractures can occur, especially in the vertebrae, causing bone pain or musculoskeletal disorders. Hypercalcemia, i.e. an increase in the level of calcium in the blood, is also observed. Faced with such symptoms, doctors order radiological examinations and, if necessary, a biopsy.

When pathological osteolysis results from another disease, it is a priority to treat that disease first.

Against bone loss itself, the most widely used drugs are from the bisphosphonate family. These molecules slow down the activity of osteoclasts, cells that break down bone, thus limiting bone loss. These medicines should be taken for a minimum of 3 to 5 years to decrease the risk of developing a hip fracture or a vertebral fracture. But there are others (Raloxifene, teriparatide, etc.), acting either on the destruction or on the construction of new bone tissue. The choice of treatment depends on the cause of the problem, and any interactions it may have with other substances. 

Adopting a better lifestyle also stimulates the formation of new bone tissue: 

• physical exercise ;
• cessation of tobacco and alcohol consumption;
• etc.