Periostitis and pseudoperiostitis.

Increased metabolic activity with the periosteum is demonstrated radiographically by the presence of a linear shadow of bone paralleling the cortex, most commonly reflecting increased osteoblastic activity and thus representing periosteal new bone. This is frequently seen in psoriatic arthritis and Reiter's syndrome. A similar picture occurs with increased osteoclastic activity and reflects rapid demineralization, simulating periostitis. This change must be recognized as a reflection of osteoporosis, lest the condition be misdiagnosed as inflammatory disease.