The three disorders described in this chapter can all result from monoclonal plasma cell proliferations; for POEMS syndrome this is exclusively so, while heavy chain disease (HCD) may be a consequence of other B-cell lymphoproliferative disorders. Cryoglobulinaemia may likewise be associated with a lymphoproliferative malignancy but is most usually seen in association with hepatitis C virus (HCV) infections. A feature they share is the production of abnormal immunoglobulins. They have all been investigated using serum free light chain (sFLC) and/or immunoglobulin heavy/light chain (Hevylite, HLC) analysis.
Cryoglobulins are serum immunoglobulins that reversibly precipitate at temperatures below 37°C. Cryoglobulinaemia is classified according to the clonality and rheumatoid factor activity of the cryoglobulin . It is associated with many illnesses, which can be broadly grouped into infections, autoimmune disorders, and malignancies. The most common cause is infection with HCV .
sFLC concentrations are elevated in many patients with monoclonal cryoglobulinaemia, and may serve as a useful tool for monitoring response to treatment since direct measurement of cryoglobulins is technically difficult. Pattenden et al.  described a case of Waldenström’s macroglobulinaemia associated with a type 1 cryoglobulin. Serum protein electrophoresis (SPE) revealed the presence of an IgMλ monoclonal protein that could not be quantitated since it precipitated out of the gel. However, serial sFLC measurements were successfully used to monitor response to chemotherapy (Chapter 32, Clinical Case History). Besada et al.  report a case of type-1 (IgGκ) cryoglobulinaemic vasculitis (treated successfully with bortezomib after rituximab failure) that was effectively monitored with sFLCs.
34.3. Heavy chain diseasesChapter 3) . The three main types are α-, γ- and μ-HCD.
Since HLC assays target junctional epitopes that span the immunoglobulin heavy and light chains (Chapter 9), the monoclonal protein associated with HCD is not recognised by HLC assays. However, in such cases, HLC assays allow quantitation of the polyclonal immunoglobulins.
Kaleta et al.  evaluated the use of IgG HLC assays in 15 patients with γ-HCD. By immunofixation electrophoresis, each patient’s serum contained a discrete γ-heavy chain with no associated κ or λ light chains (Figure 34.1A). The concentration of polyclonal IgG (determined by HLC analysis: IgGκ + IgGλ) accounted for 18% of the total IgG (as measured by a total IgG nephelometric assay). This indicated that 82% of the IgG did not have an associated light chain. Subtraction of IgGκ + IgGλ HLC concentrations from total IgG measurements was an indirect measure of the monoclonal heavy chain produced by the tumour . The relationship between the heavy chain concentration determined by this indirect nephelometric measure was compared with that determined by SPE (using scanning densitometry) (Figure 34.1B). The monoclonal protein concentration determined by nephelometry was approximately 2-fold higher than the value determined by SPE. This overestimation of total IgG may be due to the calibrator comparing poorly with the monoclonal heavy chain fragment.
Although no light chains are bound to monoclonal heavy chains, monoclonal sFLCs have been reported . In a study of 15 patients with γ-HCD, 20% had monoclonal κ sFLCs . This finding was supported by flow cytometry of tumour cells from a patient with γ-HCD plus monoclonal κ sFLCs where the tumour cells were positive for cytoplasmic IgG with κ restriction . This indicated that the tumour was the source of both the monoclonal γ-heavy chain and κ sFLCs. Deighan et al.  reported an unusual case study of a multiple myeloma (MM) patient with a triple monoclonal gammopathy: IgGκ, κ sFLCs and γ-heavy chains. The patient was monitored with a combination of electrophoresis, Freelite and Hevylite assays, and enabled the patient’s disease evolution to be fully characterised. The patient was initially diagnosed with IgGκ MGUS, and evolved through to MM with both light chain and γ-heavy chain escape. The authors conclude that the potential for heavy chain escape should be kept in mind when monitoring MM patients.
34.4. POEMS syndrome
POEMS syndrome is a rare paraneoplastic syndrome related to an underlying plasma cell disorder (PCD) that is monoclonal λ-restricted in >95% of cases . The term POEMS is an acronym encompassing the features Polyneuropathy, Organomegaly, Endocrinopathy, Monoclonal PCD, and Skin changes. However, not all of these features are required to make a diagnosis, and there are other additional important clinical features not covered by the acronym (such as elevated vascular endothelial growth factor [VEGF] levels, sclerotic bone lesions, extravascular volume overload and Castleman disease) . Whilst the pathogenesis of the condition is poorly understood, increased levels of cytokines (including VEGF) are thought to play a major role .
Although SPE and sFLC analysis constitute a simple and efficient diagnostic screen for the majority of monoclonal gammopathies (Chapter 23), the diagnostic sensitivity of this algorithm is inadequate for POEMS syndrome, where the monoclonal protein production is often small (median 1.1 g/L) . A large screening study by Katzmann et al. concluded that serum immunofixation electrophoresis (sIFE) should be performed in addition to SPE and sFLC analysis when a diagnosis of POEMS syndrome is suspected , whereas the European Myeloma Network recommend sIFE, uIFE and FLC testing to evaluate patients with suspected POEMS syndrome .
Stankowski-Drengler et al.  studied sFLC measurements in 50 patients with newly diagnosed POEMS syndrome. In all cases the involved FLC type was λ. Forty-five patients (90%) had elevated λ sFLCs, 34 (68%) had elevated κ sFLCs, but only nine (18%) had abnormal sFLC ratios. Similar findings were reported by Wang et al. who characterised sFLC measurements in a Chinese population comprising 90 newly diagnosed POEMS patients. Both studies concluded that polyclonal FLC elevations in POEMS syndrome may be due to renal impairment and/or polyclonal activation of B-cells (Section 6.2) . In such conditions, elevated polyclonal κ sFLCs neutralise the abnormal sFLC ratio induced by the subtle production of monoclonal λ sFLCs.
Wang et al.  studied the utility of HLC analysis in a large group of 90 patients with POEMS syndrome (58 IgA, 30 IgG and 2 light chain only). An abnormal IgA HLC ratio was present in 79% (46/58) IgA patients and also one of the light chain only patients. In comparison, an abnormal IgG HLC ratio was present in 63% (19/30) IgG patients. When all patients were considered, the incidence of HLC pair suppression increased along with the monoclonal protein concentration, from 14% in patients without a quantifiable monoclonal protein, to 44% in subjects with a monoclonal protein >5 g/L (p=0.039). An abnormal HLC ratio predicted clinical relapse, when measured either at baseline or after treatment, and the significance increased when more extreme ratios were considered (both p<0.001).
Altinier et al.  compared involved HLC and VEGF concentrations during follow-up for 7 POEMS patients: HLC showed a reasonable agreement with VEGF throughout the monitoring period. This was in contrast to the involved FLC values, which showed a poor correlation with VEGF.
In summary, initial data suggest that HLC assays identify disease clonality in the majority of POEMS patients, and HLC analysis may have prognostic value.