What is POH: Progressive Osseous Heteroplasia?

Introduction to POH | Symptoms of POH | Solving the Mystery of Extra Bone

Introduction to POH

Progressive Osseous Heteroplasia (POH) is a rare genetic condition in which the body makes extra bone in locations where bone should not form. Extra bone develops inside skin, subcutaneous tissue (fat tissue beneath the skin), muscles, tendons, and ligaments. This ”out of place extra bone formation” is commonly referred to as heterotopic ossification. In people with POH, nodules and lace-like webs of extra bone extend from the skin into the subcutaneous fat and deep connective tissues, and may cross joints. Extra bone formation near the joints may lead to stiffness, locking, and permanent immobility.

Symptoms of POH

The condition is often first noted in infancy with the appearance of small “rice-grain” particles of bone in the skin. A parent may describe this as a roughness in the skin. During childhood, bone formation may progress from the skin into subcutaneous tissue and extend into deeper structures including muscles, tendon and ligament. Affected areas may be small or large and involve scattered and variable regions of the body surface. The condition does not involve any other organ system and does not affect the formation of any portions of the normal skeleton at birth.

POH is often congenital, meaning that it may be present at birth. In most children symptoms of POH usually begin during the first few months of life. The majority of affected children are diagnosed with POH before the age of ten.

Bone formation begins typically in small patches of skin and can occur in any region of the body. People who have POH experience different rates of new bone formation: in some, the progress is rapid, while in most it is more gradual. In each child, the exact rate of progression is unpredictable. In any affected area, there appears to be a progression from superficial to deeper tissues. For example, extra bone formation occurs first in the skin, then progresses down to subcutaneous tissue, and then to deeper tissues like muscle. In some individuals, the bone formation may involve a small area of the body, and in others, relatively large or multiple areas of the body. Very often, the extra bone formation may predominate more on one side of the body. Although the limbs are most commonly affected, bone formation may also involve the head, chest, abdomen, pelvis and back.

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