Mu-Heavy Chain Disease
A type of HCD characterized by the production of incomplete monoclonal mu-heavy chains without associated light chains. The clinical presentation resembles that of patients with chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL).
Epidemiology
The prevalence is unknown but the disease is extremely rare. Only about 35 cases have been reported in the world literature.
Clinical description
The age at diagnosis is usually between 50 and 60 years. The most common presenting symptoms are those of a lymphoproliferative malignancy although peripheral lymphadenopathy is less common than in CLL. Lytic bone lesions and osteoporosis have been reported in a few cases.
Etiology
The cause of mu-HCD is unknown.
Diagnostic methods
The diagnosis of mu-HCD is made by documentation of the abnormal heavy chain by immunofixation of serum and urine. Unlike alpha- and gamma-HCD, some patients with mu-HCD have increased free light chain secretion (Bence Jones proteinuria). Examination of the bone-marrow shows an increase in lymphocytes, plasma cells, or plasmacytoid lymphocytes.
Differential diagnosis
The differential diagnosis of mu-HCD includes all lymphoplasma-cell proliferative disorders. Without a suspicion for the disease, mu-HCD is difficult to diagnose. The finding of Bence Jones proteinuria in a patient with a lymphoproliferative disorder and vacuolated plasma cells in the bone marrow deserves further investigation for possible mu-HCD.
Management and treatment
There is no specific treatment for mu-HCD. If mu-HCD protein is found in the serum of an asymptomatic patient this should be followed closely for the development of a symptomatic lymphoplasma-cell proliferative disorder. Treatment of symptomatic patients with mu-HCD is similar to that employed in patients with CLL (eg, glucocorticoids, alkylating agents).
Prognosis
The disease course and prognosis seen in mu-HCD is highly variable. The median survival from time of diagnosis is 24 months and ranges from < 1 month to 11 years.