The author describes the clinical, electrophysiological, and pathological phenotype of neuropathies associated with anti-GD1b antibodies, frequently manifested by prominent ataxia. These may arise as acute post-infectious syndromes or as chronic paraproteinemia-associated syndromes. Recently, antibodies that bind to complexes of GD1b with GD1a, but not to either ganglioside alone, have been identified in a proportion of Guillain Barré syndrome sera, underlining the complexity of how antibodies are able to sense their target antigens in neural membranes. Some patients have been successfully treated with intravenous immunoglobulin and rituximab.
• In patients with chronic ataxic neuropathy and IgM paraproteinaemia, screening for CANOMAD should be considered.
• CANOMAD may exist in formes frustes where not all clinical or laboratory components are manifested.
• Identification of syndromes associated with an anti-GD1b antibody biomarker should alert clinicians to a potentially treatable disorder.
Historical note and terminology
In the early 1980s many clinical and serological studies started focusing on peripheral neuropathy syndromes associated with IgM paraproteinemia. Paraproteins have also been referred to as M-proteins or (benign) monoclonal gammopathies. The specificities of these paraproteins were almost invariably found to be directed to carbohydrate determinants present on different glycoproteins and glycolipids distributed in neural tissue. The first to be identified were myelin-associated glycoprotein and structurally related glucuronic acid-containing acidic glycosphingolipids (Quarles 1997).
In 1985 a case of IgM paraproteinemic neuropathy in which the paraprotein reacted with NeuNAc(alpha2-8)NeuNAc(alpha2-3) configured disialylated gangliosides including GD1b, GD3, GD2, and GT1a, GT1b, and GQ1b was reported (Ilyas et al 1985). Following this report, several other cases similarly characterized by a chronic sensory ataxic neuropathy were reported in the early 1990s (Arai et al 1992; Duane et al 1992; Obi et al 1992; Younes-Chennoufi et al 1992; Yuki et al 1992; Willison et al 1993; Herron et al 1994; Hitoshi et al 1994). A series of 18 cases was reported in 2001 that describes the syndrome more completely (Willison et al 2001). It is now apparent that this syndrome represents a relatively pure clinical-serological phenotype, dominated by sensory ataxia without functionally substantial limb weakness in most cases. Terminologically, these cases have been referred to variously as sensory neuropathy, sensory ataxic neuropathy, peripheral neuropathy, or ataxic neuropathy with anti-GD1b, anti-disialosyl, or anti-B series ganglioside antibodies.
In some cases the IgM paraprotein also has cold agglutinating activity with anti-Pr specificity (Arai et al 1992; Willison et al 1993; Herron et al 1994). In other cases craniobulbar motor involvement, including ophthalmoplegia, may also be present (Ilyas et al 1992; Herron et al 1994). To reflect this, in 1996 the acronym CANOMAD was coined to encompass this phenotype, chronic ataxic neuropathy with ophthalmoplegia, M-protein, agglutination and disialosyl antibodies (Willison et al 1996). Although this acronym is useful as an aide memoir when considering potential cases, it should be appreciated that not all cases exhibit the full spectrum of clinical features. In a Japanese series of 5 cases of sensory ataxic neuropathy with anti-GD1b antibodies and IgM paraproteinemia, all patients had severe sensory ataxia and areflexia, but only 1 of the 5 cases manifested a transient diplopia on lateral gaze and 2 of the 5 cases had cold agglutinins (Susuki et al 2001). In contrast, 2 cases reported as part of a long-term follow-up of paraproteinemic neuropathy cases had all the features of CANOMAD (Ponsford et al 2000).
In a large series of 18 cases (Willison et al 2001), the syndrome was described as a chronic sensory ataxic neuropathy with anti-disialosyl antibodies, and cases showed remarkable clinical homogeneity, as described below.
Acute phase anti-GD1b IgG antibodies have been identified in isolated patients with acute sensory neuropathies, acute ataxic neuropathies, or both, without limb weakness, which is considered a forme fruste or regional variant of Guillain Barré syndrome (Willison and Veitch 1994; Yuki and Hirata 1998; Willison and Yuki 2002). Some patients with Miller Fisher syndrome (or Fisher syndrome) also have anti-GD1b antibodies by virtue of their cross-reactivity with anti-GQ1b/GT1a antibodies, which are universally found in this syndrome (Chiba et al 1992; Willison and Veitch 1994; Susuki et al 2001). In addition, it has been observed that GD1b antibodies are statistically associated with sensory symptoms in Guillain Barré syndrome (Wicklein et al 1997) and with ataxia (Kaida et al 2008). A recent clinical and serological review of patients with ataxic Guillain Barré syndrome and acute sensory ataxia has concluded that this clinical syndrome represents an incomplete forme fruste of Miller Fisher syndrome (Ito et al 2011). Antibodies to GD1b/GD1a ganglioside complexes are present in a proportion of Guillain-Barré syndrome cases (Kaida et al 2004). Thus, the spectrum of sensory neuropathies associated with anti-GD1b antibodies has expanded to both chronic and acute disorders, the former being associated with IgM paraproteins and the latter with acute phase, transient IgG antibodies. This topic focuses on the IgM paraproteinemia-associated syndromes.
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