While MGUS and Kidney disease is now a finding well described in the literature, why not other organs?
It is quite possible that there is end organ damage to other organs from these small set of B cell or plasma cell clones if there is kidney damage.
A recent review in the corneal world found a case series of what we could call MIDD in the cornea. Seven patients were identified with corneal immunoglobulin deposition. The structures they found are similar to crystalline structures. Some of them looked like immunotactoid, some fibrillary and some amyloid. All patients had evidence of paraproteinemia in a setting of monoclonal gammopathy of undetermined significance, smoldering plasma cell myeloma, or Waldenström macroglobulinemia. Authors suggest treating underlying MGUS or paraprotein disease. Few patients, this was the first systemic presentation of the disease. What a great observation!! If it can effect small renal vessels, why not the eye!
What other organs?
Skin: The association between Necrobiotic xanthogranuloma(NXG) and paraproteinemia is well documented in 2009. 11-48% had paraprotein disease as myeloma. The most common is IgG kappa more than lambda. However, the skin lesions in NXG could represent reactive inflammation and are not associated with the presence of monoclonal plasma cells or multiple myeloma.
Powell et al also described initially eight patients with pyoderma gangrenosum and monoclonal gammopathy showed that all patients except one had an IgA paraproteinemia. Seven patients have had a benign course and multiple myeloma has developed in one. In seven patients, the onset of thepyoderma gangrenosum preceded the detection of the monoclonal gammopathy. Since then, more cases have been associated with MGUS.
Besides POEMS syndrome, which has been well described in the literature, others are :
TEMPI syndrome, a syndrome that was mentioned in NEJM that had a constellation of findings: Telangiectasias,elevated erythropoietin level and erythrocytosis, monoclonal gammopathy(IgG kappa), perinephric fluid collections and intrapulmonary shunting. Since it’s initially discovery, chemotherapy and HSCT have been used for treatment of this entity.
Schnitzler's syndrome, initially described in 1974 is an uncommon condition defined by chronic urticaria and monoclonal IgM gammopathy. A study done in 2002 found 56 cases of Schnitzler's syndrome reported to date. The absence of lymphoproliferative disease in this condition is typical, but nine patients have progressed to develop lymphoplasmacytic neoplasias, particularly waldenstrom's macroglobulinemia.
So, besides MGRS, MGUS might have other distant organ effects from small noxious B cell clones. Perhaps, this needs to be defined more and treated more like MGRS. It might be interesting to see the cases of ITG and fibrillary GN – if they have corneal findings and other end organ damages that we might be missing given these novel associations. We might be looking at a more systemic disease.
We might be entering a new era in the paraprotein world.