Written by Professor J M Connor MD, FRCP for the Muscular Dystrophy Campaign.
Myositis ossificans progressiva, also known as Fibrodysplasia ossificans progressiva or FOP, is a disabling condition which is caused by the formation of bony bars within the muscles of the body. This bone formation is usually first noticed in early childhood as a series of hard lumps in the neck or along the spine. These lumps, which may be tender, gradually shrink in size as the affected muscles are replaced by bone. The appearance of bony lumps in muscles is usually spontaneous but can also be provoked by any injury to the muscles. Disability in MOP is physical and very variable in extent; intelligence in unaffected.
How does the condition progress?
MOP is progressive in that more muscles become involved with increasing age, but the rate of progression is very variable from one person to another. Furthermore, the condition tends to show long periods of inactivity (of up to several years in length).
Can any muscles be affected?
Certain muscles are never involved in this disease. These include the muscles of the eyes, the face, the tongue, the gullet, the intestines and the muscles of continence (bowel and bladder control). The heart is never involved in this condition. Chest expansion may be reduced in MOP but the diaphragm, which is the single most important breathing muscle is never involved.
What is the life-span of people who have MOP?
General health remains good and several people with MOP in Britain are over 60 years old.
Are there any other features of MOP?
Most people affected by MOP have some abnormalities of the fingers or toes. The toes are most commonly involved and are often shortened and deviated. These differences are usually apparent at birth.
How common is MOP?
This disorder occurs in all countries in the world and affects about one person in a million. Men and women seem to be equally affected.
Is MOP hereditary?
The basic genetic error is thought to occur at the moment of conception. The chance of it happening is very low and is certainly less than one in a million if both parents are unaffected. For a person with MOP, however, there will be a one in two chance of handing on the condition to any children. Further information on this point may be obtained from your local genetic counselling clinic.
Is there a treatment?
Many types of treatment have been tried in the past and none of these has been shown to be of benefit. A number of medications are being evaluated at present and if any of these is shown to be of clear benefit then everyone with MOP will be contacted directly.
Does anything make MOP worse?
Injury to the muscles can often provoke local bone formation. For this reason intramuscular injections should be avoided if possible. Similarly operations on the muscles to remove pieces of bone almost invariably result in increased bone formation. Also, some forms of dental treatment may result in bone formation in the jaw muscles and you should therefore warn your dentist that you have MOP.