Rare diseases

First classification criteria set for IgG4-related disease

The first ACR/EULAR Classification Criteria for IgG-Related Disease (IgG4-RD) has achieved a high specificity of 97.8% and sensitivity of 82% in the final validation cohort of 485 patients. 

Published in Arthritis & Rheumatology, the criteria provide a useful framework for clinicians considering the diagnosis but will have most relevance to researchers interested in the relatively recently recognised multiorgan disease.

“These criteria are not intended for use in clinical practice as the basis of establishing the diagnosis of IgG4-RD,” the document said. 

“The purpose of these classification criteria is to facilitate the identification of more homogeneous groups of subjects for inclusion into clinical trials and observational studies.”

The development and testing of the classification criteria involved the input of 86 international investigators and multiple rounds of validation in patient cohorts. 

The 3-step classification process includes entry, absolute exclusion and weighted inclusion criteria. 

“A case meets the classification criteria for IgG4-RD if the entry criteria are met, no exclusion criteria are present, and the total points [for inclusion criteria] is ≥20.”

“An important strength of this criteria set is that a patient may be classified accurately as having IgG4-RD in many cases even in the absence of a biopsy.” 

“Although biopsies are essential in many settings to establish the diagnosis of IgG4-RD and exclude mimickers, we aimed to develop criteria in which biopsy is not required when the diagnosis of IgG4-RD is straightforward on the basis of clinical, serologic, and radiologic findings. Such criteria are consistent with clinical practice, compatible with research, and essential to the appropriate diagnosis of patients in both clinical and research settings.”

The Classification Criteria Working Group found that nearly 20% of cases classified as IgG4-RD had a normal serum IgG4 concentration or did not have a serum IgG4 value available. 

“Moreover, 9% of the IgG4-RD cases did not have a biopsy, 37% lacked the classic histopathologic findings, and >40% did not meet previously defined cutoffs for IgG4+ plasma cell infiltrates.” 

“These criteria reflect the reality of clinical care and clinical investigation in IgG4-RD; clinicians consider a combination of factors when determining whether to classify a patient as having this disease.”

Professor John Stone, from Harvard Medical School and director of the working group, said IgG4-RD was now recognised to be “a worldwide condition that is seen not only by rheumatologists but also generalists and sub-specialists of nearly every kind”.

He added the criteria should be a highly useful contribution to future investigations and will ultimately help improve the lives of patients with IgG4-RD.

“Clinical trials will help develop targeted therapies that spare toxicities from conventional treatments. Investigators need to have criteria like this to determine whether a patient should be classified as having IgG4-RD.”

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