Hematology

	Answer 5 Anti-MAG antibodies. This patient’s symptoms of distal peripheral sensory neuropathy are strongly suggestive of the demyelinating condition caused by IgM MGUS with anti-MAG reactivity. Anti-MAG antibodies are the most common form of antineuronal autoantibodies. Other types include antisulfoglucuronyl paragloboside, antiganglioside (GM1 and GM2), and antidisialosyl ganglioside (GD1b and GT1b) antibodies.6 Although up to half of patients with WM may have some degree of peripheral neuropathy (occasionally due to anti-MAG specificity of the WM M-protein), only 10% of patients with an antineuronal antibody are subsequently found to have an underlying lymphoproliferative condition.6 The absence of lymphadenopathy, abnormal blood counts, or organomegaly makes WM unlikely. There are also no findings to suggest myeloma, which is almost never associated with an IgM M-protein. Amyloidosis, a plasma cell dyscrasia usually associated with self-aggregating λ light chains, could be a consideration. If the patient had symptoms of congestive heart failure, tongue enlargement, renal dysfunction, or easy bruising often associated with amyloidosis, a fat pad aspirate with Congo red staining would be appropriate, but this is not the case in this patient. Guillain-Barré syndrome typically presents as an acute-onset, rapidly progressive, ascending motor neuropathy without significant sensory loss. The patient does not have findings to suggest POEMS syndrome (Polyneuropathy, Organomegaly, Endocrinopathy, M-protein [usually λ-restricted IgG or IgA, in contrast to the IgM-κ seen in this patient], and Skin changes/sclerotic bone lesions). At a minimum, a diagnosis of POEMS syndrome requires polyneuropathy, a plasmaproliferative process, and 1 other criterion included in the acronym “POEMS” or concurrent Castleman disease. REFERENCES 6.  Lozeron P, Adams D. Monoclonal gammopathy and neuropathy. Curr Opin Neurol 2007;20:536-41. Click here to return to the questions
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