Pustulotic arthro-osteitis associated with palmoplantar pustulosis

Palmoplantar pustulosis (PPP) is a chronic inflammatory disorder characterized by sterile pustules predominantly involving the palms and soles of middle-aged women. PPP frequently develops or exacerbates following focal infections, such as tonsillitis, odontogenic infection and sinusitis, either with or without arthralgia and/or extra-palmoplantar lesions. Pustulotic arthro-osteitis (PAO) is a joint comorbidity of PPP, most often affecting the anterior chest wall. PAO is sometimes regarded as the same entity as synovitis, acne, pustulosis, hyperostosis and osteitis (SAPHO) syndrome, and may be a subtype or incomplete type of SAPHO syndrome; however, there are several differences. In Japanese patients, PPP with PAO is frequently seen, whereas SAPHO syndrome in the true meaning is rare. A difference of incidence depending on race suggests that different genetic backgrounds may be responsible for susceptibility to these disorders. Bacterial infection, especially Propionibacterium acnes, is suggested to play an important role in the pathogenesis of SAPHO syndrome. P. acnes is responsible for acne, however, bacterium is unassociated with PPP skin lesions which are characterized by sterile pustules. On the other hand, PAO is frequently triggered by focal infection, and treatment of focal infection results in dramatic effects on the release of joint pain. This paper reviews current insights into the clinicopathophysiology of PAO, and discusses its possible mechanisms in comparison with SAPHO syndrome.