Relationship between inflammation and joint destruction in early RA: a mathematical description

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Ann Rheum Dis. 2004 Jul;63(7):848-52.

Relationship between inflammation and joint destruction in early

rheumatoid arthritis: a mathematical description.

Wick MC, Lindblad S, Klareskog L, Van Vollenhoven RF.

Rheumatology Unit, Department of Medicine, Karolinska Hospital, S-171 76

Stockholm, Sweden; marius.wick@...

BACKGROUND: The relationship between inflammation and joint destruction

in rheumatoid arthritis (RA) has not been unequivocally characterised.

Joint destruction may result from the cumulative inflammatory burden

over time, modified by an individual constant factor. OBJECTIVE: To test

the hypothesis that the relationship between radiological progression

and inflammation can mathematically be expressed as:where Re is a factor

that varies from person to person. METHODS: Clinical data and

radiographs of 76 patients with early RA receiving different disease

modifying antirheumatic drugs were analysed. Radiographs were quantified

using the modified Larsen score and the " X-Ray RheumaCoach " software.

The cumulative inflammatory burden was estimated by the time integrated

28 joint Disease Activity Score (DAS28), calculated as the area under

the curve. RESULTS: 76 patients with early RA who started treatment with

methotrexate (n = 20), sulfasalazine (n = 37), or oral gold (n = 19)

monotherapy were evaluated. The mean (SEM) DAS28 decreased from 4.6

(0.1) at baseline to 2.3 (0.1) after 2 years. The mean (SEM) DeltaLarsen

score from baseline to year 2 was 10.3 (1.5). Correlation between

cumulative inflammation and radiographic change was poor. In contrast,

when calculating a person's factor Re in year 1 ( Re 1) and year 2 ( Re

2), a strong and significant correlation (r = 0.58, p<0.000001) was seen

between Re 1 and Re 2.

CONCLUSIONS: Joint destruction is the result of the cumulative burden of

inflammation over time, modified by an individual factor Re that remains

relatively constant over the first 2 years of observation. The data

support a mathematical model that expresses the interrelationship

between inflammation and joint destruction.

PMID: 15194582

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