IgG4, the Great Mimicker, But With These Tips You Can Figure it Out!

On Thursday morning, Dr. Mollie Carruthers led a case-based workshop on what to do with a 66-year-old man who has intermittent submandibular gland swelling, pancreatitis and IgG4 elevation.

The differential could be lymphoma, Sjogren's, IgG4, etc. He had pancreatitis, so pancreatitic cancer had to be ruled out.

Clinical Pearls: Differentiate IgG4 from other autoimmune rheumatologic diseases and if there is pancreatic involvement, differentiate from pancreatitc cancer.

• IgG4 disease does not have anti-Ro and -La (SSA/SSB)

• Sjogren's may have hypergammaglobulinemia but not IgG4 marked elevation

• IgG4 disease may have elevation of IgG4 subtype but this is NOT mandatory and not specific 

  • 50% of patients with IgG4 disease have normal IgG4 serum levels

• Staining of IgG4 on biopsy is key

  • Don't be misled – get tissue and let the pathologist know what you are looking for since there are criteria for staining based on the amount of IgG4 present, and relative ratio vs. other Ig's

• If other serious organ involvement is suspected or needs to be characterizied you may consider pan-imaging (but in my opinion a PanCT on all IgG4 patients may find asymptomatic involvement but is a lot of radiation; I don't know how good MRI is)

• Imaging may help to profile what organs/tissues are involved and see what requires follow-up or treatment

• Ocular involvement with proptosis can suggest pseudotumour and mimic GPA orbital involvement
  

• Relapse rate of autoimmune pancreatitis is 30%

• (I think but the speaker did not say this: Sjogren's and IgG4 both can have autoimmune pancreatitis)

Organ involvement

Be systematic on history and physical exam from head to toe (bolded items are the most common) – lymphadenopathy, submandibular gland, autoimmune pancreatitis, retro-orbital fibrosis, retroperitoneal fibrosis, obliteration of blood vessels, pulmonary, aorta (aoritis), thyroid (Riedel's thyroiditis), orbital pseudotumour, can get myositis of ocular muscles, parotid, prostatitis, cholecystitis, mediastinitis, etc.

Treatment

Much of IgG4 treatment is based on autoimmune pancreatitis related to IgG4 data. Initiate prednisone at 30 mg PO QD and slowly taper.

If there is other significant involvement: 

• Steroids

• Conventional DMARDs: Azathioprine and  mycophenolate mofetil  (MMF may be better than AZA). Second-line DMARDs (less studied) include methotrexate and cyclophosphamide. 

• Rituximab

Consensus for IgG4 pathology

Presence of 2 of 3 of the following: 

• Lymphoplasmacytic infiltrate

• Fibrosis

• Obliterative phlebitis

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