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.”[2]It is associated with GNAS.
[5] Patients with POH have a distinctly different manifestation of symptoms than those with fibrodysplasia ossificans progressiva (FOP), though heterotopic ossification appears in both diseases.
They lack the congenital abnormality of the big toe that is a diagnostic feature for FOP.
Also, the pattern of ossification differs in POH, spreading in an intramembranous fashion rather than endochondral.