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DEFINITION

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  • The heavy-chain diseases (HCDs) are neoplastic disorders of B cells that produce monoclonal immunoglobulins (Ig) consisting of truncated heavy chains without attached light chains.

  • The diagnosis is established from immunofixation of serum, urine, or secretory fluids in the case of α-HCD or from immunohistologic analysis of the proliferating lymphoplasmacytic cells in nonsecretory disease.

  • In decreasing order of incidence, HCD involves synthesis of defective α, γ, or μ heavy chains.

  • There is a high frequency of autoimmune disorders preceding or concurrent with the diagnosis of HCD, particularly γ-HCD.

  • Table 71–1 summarizes the clinical features of the three types of HCD.

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TABLE 71–1SUMMARY OF FEATURES OF THE HEAVY-CHAIN DISEASES
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ETIOLOGY AND PATHOGENESIS

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  • The etiology of γ-HCD and μ-HCD is unknown.

  • In α-HCD, the lymphoplasmacytic infiltration of the intestinal mucosa is thought to be a response of the alimentary tract immune system to protracted luminal antigenic stimulation.

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CLINICAL AND LABORATORY FEATURES

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γ-HCD

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  • Median age at presentation is in the late sixties.

  • Clinical features different from those of myeloma because renal disease and osteolytic lesions rarely occur.

  • Has various clinical and pathologic features that can be divided into three broad categories:

    — Disseminated lymphoproliferative disease.

    — Localized proliferative disease: Approximately 25 percent of patients.

    — No apparent proliferative disease: Approximately 15 percent of patients.

  • Most γ-HCD proteins are dimers of truncated heavy chains without associated light chains.

  • The serum protein electrophoretic pattern is extremely variable, but a monoclonal peak is detected in over two-thirds of patients.

  • The median value of the monoclonal spike at diagnosis in one study of 19 patients was 1.6 g/dL.

  • The amount of HCD protein in the urine usually is small (<1 g/24 h), but may reach 20 g/24 h.

  • Patients commonly have moderate, normochromic, normocytic anemia.

  • Autoimmune hemolytic anemia has been reported.

  • Bone lesions are rare.

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