= MYOSITIS OSSIFICANS PROGRESSIVA (misnomer since primarily connective tissues are affected)

= rare slowly progressive sporadic / autosomal dominant disease with variable penetrance characterized by remissions + exacerbations of fibroblastic proliferation, subsequent calcification + ossification of subcutaneous fat, skeletal muscle, tendons, aponeuroses, ligaments

Histo: edema with proliferating fibroblasts in a loose myxoid matrix; subsequent collagen deposition plus calcification + ossification of collagenized fibrous tissue in the center of nodules

Age: presenting by age 2 years (50%)

• initially subcutaneous painful masses on neck, shoulders, upper extremities
• progressive involvement of remaining musculature of back, chest, abdomen, lower extremities
• lesions may ulcerate and bleed
• muscles of back + proximal extremity become rigid followed by thoracic kyphosis
• inanition ← jaw trismus (masseter, temporal muscle)
• “wry neck” = torticollis ← restriction of sternocleidomastoid m.
• respiratory failure ← thoracic muscles affected
• conductive hearing loss ← fusion of middle ear ossicles

1. ECTOPIC OSSIFICATION
   • rounded / linear calcification in neck / shoulders, para-vertebral region, hips, proximal extremity, trunk, palmar and plantar fascia forming ossified bars + bony bridges
   • ossification of voluntary muscles, complete by 20–25 years (sparing of sphincters + head)
2. SKELETAL ANOMALIES
   may appear before ectopic ossification
   • clinodactyly
   • microdactyly of big toes (90%) and thumbs (50%)
     = usually only one large phalanx present / synostosis of metacarpal + proximal phalanx (first sign)
   • phalangeal shortening of hand + foot (middle phalanx of 5^th digit)
   • shortened 1^st metatarsal + hallux valgus (75%)
   • shortened metacarpals + metatarsals
   • shallow acetabulum
   • short widened femoral neck
   • thickening of medial cortex of tibia
   • progressive fusion of posterior arches of cervical spine
   • narrowed AP diameter of cervical + lumbar vertebral bodies
   • ± bony ankylosis

CAVE: surgery is hazardous causing accelerated ossification at the surgical site