Erosions versus joint space narrowing in rheumatoid arthritis: what do we know?

Both erosions and joint space narrowing (JSN) are aspects of structural damage in rheumatoid arthritis. Most information is available on structural damage as one concept. However, the differential aspect of the effects on bone and cartilage could yield interesting information. Comparative information of these aspects can be based only on radiographic data on erosions and JSN. Both erosions and JSN are the consequence of inflammation, and their progression is inhibited by drugs that inhibit inflammation. These two processes often occur in parallel but joints in which erosions are present show a preference for progression of erosions and, to a lesser extent, development of JSN. The reverse is true for joints with JSN present, where there is a preference for worsening of JSN over development of erosions. Repair is possible for erosions as well as JSN and this is related to the absence of inflammation and effective treatment (especially methotrexate in combination with a tumour necrosis factor blocker).