Bone manifestations of SM: Part One

Osteoporosis is a progressive condition in which bone mass and density decreases. This leads to a greater risk of fracture, often fragility fractures, in which a bone breaks from normal activities like a small fall. These breaks usually affect the vertebrae, neck of the femur, wrist (Colles fracture) and ribs. Osteoporosis is defined as bone mineral density 2.5X less than the mean peak bone mass. Osteoporosis has no symptoms in and of itself.

Osteopenia is a decrease in bone mass. It is essentially pre-osteoporosis.

Osteosclerosis is an increase in bone density. This can occur when there has been damage to nearby bone and it has been crushed together into one smaller area.

Osteopetrosis is also an increase in bone density. It may lead to osteosclerosis. In osteopetrosis patients, it is due specifically to a rare genetic disorder.

Osteolysis is the active resorption of bone by osteoclasts. This means that the bone cells are essentially eating the bone away.

Osteoblasts are cells that make bone. Osteoclasts are cells that resorb bone. Your body usually resorbs bone and then puts new bone in the place it resorbed. This allows your body to repair bones.

Trabecular bone is found at the ends of long bones and in vertebrae. It is spongier kind of bone with more bone remodeling and turnover. These weaker places break more easily and are commonly affected in osteoporosis.

All of the conditions listed above are basically imbalances in the processes of bone resorption and formation. In osteopetrosis, the body is depositing bone more quickly than it is resorbing it. In osteosclerosis, more mineral is present in the bone than normal. This is usually caused by damage to the bone by trauma, osteoarthritis or other causes. Osteoporosis is usually the result of one of three mechanisms: excessive resorption of bone, deficient deposition of new bone when remodeling, or disuse, in which lack of mechanical stress on the bone causes bone loss (such as in people in bed rest.) Osteolysis is when your body actively and excessively resorbs the bone. It is a marker associated with severity in several blood disorders and cancers.

55% of Americans over the age of 50 have osteoporosis. 80% of those with osteoporosis are women. Osteoporosis can be caused by a variety of factors, including prolonged use of corticosteroids or several other medications, smoking tobacco, and post-menopausal estrogen deficiency. It is also found secondary to a large number of disorders, including mastocytosis.

Systemic mastocytosis patients who have one or more C findings are considered to have aggressive systemic mastocytosis (ASM), a more severe presentation with shorter expected lifespan. One of these C findings is “bone lesions with large sized osteolyses or/and severe osteoporosis with consecutive pathologic fractures.” Pathologic fractures are bone breaks caused by bone changes due to disease that caused weakness in the bone.

Due to the fact that osteoporosis is so common, there are a number of patients with ISM who have osteoporosis. It is only considered a C finding if it is severe, with multiple fractures due to bone damage, and cannot be attributable to any other cause. It is only a C finding if mastocytosis is the reason the bones are damaged to the point of repeat fractures. In particular, prominent mast cell physicians have spoken out against the inclusion of simple osteoporosis as a C finding, particularly because the risk can be modified with therapy and does not indicate poorer prognosis. Osteoporotic vertebral fractures are particularly prevalent in ISM patients. In one study, of 20% of SM patients with osteoporosis, 18.7% had affected spines compared to 2.5% with affected hip bones.

In SM, the presence of extra mast cells in the bone causes an increase in osteoclasts, which contributes to osteopenia and osteoporosis. Histamine, heparin, TNF, IL-1 and IL-6 are all mast cell mediators known to stimulate osteoclast action. In particular, histamine acts directly on osteoclasts and osteoclast precursors.