A primary extranodal lymphoma associated with IgM‐κ paraproteinaemia: Different secretory capacities of cutaneous and circulating lymphoma cells

We report a patient with non-Hodgkin's lymphoma of small lymphocytic type with IgM-κ monoclonal gammopathy who developed extranodal involvement with orbital and nasal manifestations, followed by generalized subcutaneous nodules. Immunological study disclosed that the peripheral blood and the subcutaneous nodule were both involved in a common monoclonal proliferation of B cells at various stages of differentiation, including secretory cells which accounted for the serum paraprotein. The secretory capacity was far greater in the peripheral blood than in the subcutaneous tissue. These clinical and immunological manifestations might reflect the physiological behaviour of a particular B cell subset which shows a preference for mucocutaneous sites to secrete IgM in the peripheral blood.