Demyelinating symmetric motor polyneuropathy with high anti‐GM1 antibody titer: Do we need to split?

An 83-year-old woman developed dropped head and posterior neck pain over 6 weeks while denying other neurological symptoms. Neurological examination showed isolated mild weakness of neck extensor muscles but was otherwise normal. Magnetic resonance imaging of the cervical spine was normal, electrophysiological studies were consistent with a myopathic process isolated to the neck extensors, and creatine kinase was 80 IU/L. A diagnosis of isolated neck extensor myopathy was made. Myasthenia gravis (MG) was ruled out by physical examination and negative anti-acetylcholine receptor antibodies, and amyotrophic lateral sclerosis (ALS) was ruled out with physical examination and electrophysiological studies. Paraspinal muscle biopsy showed rare interstitial mononuclear inflammation, groups of atrophic fibers and internalized myonuclei (Fig. 1A), and scattered rimmed vacuoles (Fig. 1B), reminiscent of inclusion-body myositis (IBM). Sections treated with Congo red stain highlighted sarcoplasmic inclusions. On ultrastructural examination there were compact, elliptical inclusions comprised of thin, 4-nm-diameter filaments with periodicity (Fig. 1C and D) lacking crosslinkage. No intranuclear inclusions were found. Over the next year she was stable and was treated only with a neck brace and analgesics. Numerous conditions are associated with dropped head syndrome. The majority of cases occur in ALS and MG. Approximately 2% of ALS patients and 3% of MG patients have head drop as the initial disease manifestation. Head drop as the primary manifestation of myopathy is rarer. Although it can be part of the clinical spectrum of adult-onset nemaline myopathy, carnitine deficiency, and adult acid maltase deficiency, it is usually accompanied by generalized weakness. A literature review yielded 4 cases of IBM with isolated head drop. All had a consistent clinical phenotype of an elderly person with relatively normal creatine kinase whose head drop was unresponsive to treatment. The skeletal muscle histology often included fibrosis, atrophy, and variable numbers of rimmed vacuoles. When electron microscopy was undertaken, unlike our case, typical intranuclear filamentous inclusions of IBM were found. The paraspinal muscles are uncommonly biopsied, but two small studies suggested their normal histology can include type I predominance, type II atrophy, ragged red fibers, and myonecrosis. No reports of normal or diseased paraspinal muscles have described inclusions resembling those seen in this case. Despite their reactivity for Congo red stain, the ultrastructure of these inclusions diverges from amyloid, as they have a shard-like arrangement and a smaller diameter (4-nm filament vs. the 7.5–10-nm amyloid filament). They bear some resemblance to Hirano bodies, which have been described rarely in skeletal muscle, but these filaments are thinner and lack cross-bridging and actin immunopositivity. In conclusion, our case of an elderly woman with isolated neck extensor myopathy and light-microscopic features of IBM demonstrated unique sarcoplasmic inclusions on ultrastructural examination, which we have termed ‘‘shard-like compact aggregates of thin filaments. ’’ In recognition of the paucity of investigation into this uncommonly biopsied muscle, it is possible that these inclusions are a normal or possibly age-related degenerative finding of the paraspinal muscles, or a hitherto undescribed form of isolated paraspinal myopathy.