The clinical value of measuring immunoglobulins when assessing penicillamine therapy in rheumatoid arthritis.

Immunoglobulins are often high in active rheumatoid arthritis and fall when treatment with a slow-acting anti-rheumatic drug is instituted. We assessed the value of monitoring immunoglobulins during penicillamine therapy; 145 patients were followed for up to 5 years, IgA, IgM and IgG levels were compared to 12 other clinical and laboratory variables on 903 occasions. Mean levels of IgA and IgG fell by 10-30%. These changes were less than with ESR or clinical measures such as articular index and duration of morning stiffness. Immunoglobulin levels showed weak correlations with other variables. Only a small number of patients had hypogammaglobulinemia. Initially, 5 cases had low IgA with subsequent falls in 3 more. Initially, 2 cases had low IgG with subsequent falls in 5 more. No patients had low IgM levels. These changes seemed clinically irrelevant. Radiological progression was related to IgA levels. Patients with persistently high rates of radiological progression had persistently higher serum IgA. We conclude that IgM gives the most "acute phase" pattern of response. IgA gives more theoretically interesting information, especially concerning radiological progression. There is only a limited amount of clinically valuable information gained from measuring immunoglobulins.