Right. I admit, I’ve never heard of this disease until this year. That is 2016.
Is it rare? Yes it is.
Do you need to know about it? Probably not.
Yet, there it is in all literature.
What is it?
It is a immune-mediated condition comprised of a collection of disorders that share particular pathologic, serologic, and clinical features.
There. See? It all makes sense now.
They all mostly share features including:
- a tumour-like swelling of involved organs
- a lymphoplasmacytic infiltrate enriched in IgG4-positive plasma cell
- a variable degree of fibrosis that has a characteristic “storiform” pattern
What do they get? A whole range of disorders, but mainly:
- Type 1 (IgG4-related) autoimmune pancreatitis (AIP)
- Sclerosing cholangitis
- Sialedinitis- Mikulicz’s disease and sclerosing sialadenitis (Küttner’s tumor)
- Retroperitoneal fibrosis – involve the infrarenal aorta and iliac arteries. Chronic inflammation and fibrotic change can involve ureters -> obstructive uropathy
- Renal involvement in 1/3
- Reidel’s thyroiditis / fibrous variant of Hashimoto’s thyroiditis
- Lung & pleural disease – visceral/parietal thickening can occur, tissues have lymphoplasmacytic infiltrates enriched in IgG4+ plasma cells. Obliterative arteritis is common
Orbital pseudotumor or proptosis
The most common finding is tubulo-interstitial nephritis. Histology shows lymphoplasmacytic rich infiltrate in the renal interstitium and fibrosis. Immunohistochemistry shows IgG4+ plasma cells.
Patients have profound hypocomplementaemia – but IgG4 binds poorly to complement. Is IgG1 or 3 responsible activating this?
A small group has IgG4-related membranous nephropathy and occurrence together with TIN is possible.
The evidence is overall poor, but:
- steroids can induce remission in 4 weeks
- Next line: Rituximab – off lable
- If RTX not available – Azathioprine or MMF -but no trials