A 78-year-old woman is referred to a rheumatologist because she has been experiencing weakness and arthralgia. She complains of a skin rash; examination shows small, red, nonblanching nodules over her legs. She has a complex medical history, including systemic lupus erythematous (SLE) and rheumatoid arthritis (RA). Initial laboratory studies are remarkable for serum polyclonal hypergammaglobulinemia and hypocomplementemia (Figure 1). A cryoprecipitate was found and immunofixation electrophoresis was conducted on the pellet to look for a cryoglobulin (Figure 2).
The correct answer is ...
Type II (mixed monoclonal IgM kappa and polyclonal IgG).
Cryoprecipitation is a technique used to determine if a patient’s serum contains immunoglobulins (Igs) that precipitate out of solution at temperatures lower than body temperature (37 degrees Celsius). Cryoglobulins are associated with symptoms such as skin lesions, Raynaud phenomenon, arthralgias, peripheral neuropathy, and glomerulonephritis. Symptomology largely depends on the type of cryoglobulinemia, as the origin of the immunoglobulins is an important consideration for etiology. Treatment of any cryoglobulinemia will focus on treating the underlying disease process. If this test is positive, a small pellet will form, like shown in Figure 2 (left panel).
That pellet is then subjected to immunofixation electrophoresis (IFE) to determine the specific Igs contained within the pellet to help with diagnosis. Distinct, discrete bands in any lane correlates to a monoclonal population of immunoglobulins of the type indicated at the bottom of the lane (G, A, M, K, or L). A smear (lacking a distinct, defined band), or homogenous staining in a given lane indicates a polyclonal population of immunoglobulins.
Type II (mixed monoclonal IgM kappa and polyclonal IgG) – This patient has a cryoglobulinemia, likely associated with her autoimmune diseases. She has a history of systemic lupus erythematous (SLE) and rheumatoid arthritis (RA), both of which can be associated with cryoglobulinemia. This patient also has an overt hypocomplementemia. Hypocomplementemia is common in SLE, due to the excess immune complexes in circulation, which will activate the classical pathway of the complement system. Hypocomplementemia (low C3 and C4) is often employed as a marker of disease activity and is included in the 2019 ACR/EULAR SLE diagnostic criteria. Low levels of C3 and C4 may also be observed in recurrent infections, where consumption of the complement components takes place, but is unlikely to be the reason in this patient’s presentation. Complement components may get trapped in the cryoprecipitate and it is not uncommon to see hypocomplementemia in types II and III cryoglobulinemia — a true chicken-and-egg scenario in this patient’s case.
On the gel in Figure 2 (middle pane), a more distinct band is observed in the M and K lanes, which represents the monoclonal IgM kappa portion of the type II cryoprecipitate. The smear in the G lane represents the polyclonal IgG population of immunoglobulins. This cryoprecipitate, therefore, is of the type II (mixed) variety.
Type I (monoclonal) – A monoclonal cryoglobulin develops in the setting of a disease process that produces a monoclonal population of immunoglobulins, such as a B-cell lineage malignancy or monoclonal gammopathy of undetermined significance (MGUS). Since this patient does not have such a disease process, and her cryoglobulin isotyping IFE gel shows a mix of monoclonal IgM kappa plus polyclonal IgG, a type I cryoglobulinemia (which is the finding of a monoclonal population of immunoglobulins without polyclonal background) can be excluded.
Type III (polyclonal) – Cryoglobulins in this type of cryoprecipitate are composed of populations of polyclonal IgG and polyclonal IgM. Patients who are most susceptible to a type III cryoprecipitate are those with autoimmune disorders. No monoclonal immunoglobulins are seen in a type III cryoprecipitate.
Negative – A negative IFE gel would show no smears or distinct bands in any of the five lanes of the gels (the right panel on Figure 2, negative control). This would suggest the pellet is formed of something other than an immunoglobulin.
Ria Fyffe-Freil, Ph.D.
Fellow, Clinical Chemistry
Maria Alice Willrich, Ph.D.
Consultant, Clinical Biochemistry
Associate Professor of Laboratory Medicine and Pathology
Mayo Clinic College of Medicine and Science