Sporadic late-onset nemaline myopathy

Sporadic late-onset nemaline myopathy, or SLONM, is a very rare disease, one of the nemaline myopathies, causing loss of muscle bulk and weakness in the legs but sparing the cranial nerves, and beginning its clinical course after age 40.[1] It was first identified in 1966 at the Mayo Clinic, by A.G. Engel,[2] and that same year W.K. Engel and J.S. Resnick noted another case that they elaborated in 1975.[3][4] The diagnosis of the disease rests on subacutely evolving weakness after age 40, normal to low CK level, a myopathic EMG with fibrillations, and often a monoclonal gammopathy. The diagnosis is confirmed by visualizing rods in cryosections on light and electron microscopy. The associated monoclonal gammopathy has an unfavorable prognosis.

Sporadic late-onset nemaline myopathy
Other namesSLONM

Presentation

Weakness in a limb-girdle distribution, hips and shoulders, after age 40 is generally the first symptom. Sometimes the weakness is predominantly distal. Head drop may also be a presenting symptom. Dysphagia may occur, as can respiratory insufficiency.

Pathophysiology

The etiology is unknown.[5] Some cases of SLONM have been comorbid with HIV infection, and others with immune disorders, and so both a viral trigger and an autoimmune disorder have been considered candidate etiologies. The monoclonal gammopathy of unknown significance (MGUS) associated with a worse prognosis also argues for an immune disorder. On electron microscopy, nemaline bodies within the affected muscle fibers may be found. These bodies are sometimes crisply rod-shaped, but can also be irregular and punctate. The rods may be found alongside atrophic muscle fibers, and may be seen arising from the thickened Z-discs of the sarcolemmae. Affected fibers may be vacuolated or lobulated.[6]

Diagnosis

The myopathic EMG demonstrates fibrillation potentials. The serum CK level will be normal or low normal. The muscle biopsy will demonstrate the nemaline rods, but as they are less than 1 µm in length they are easily overlooked. The sections must be trichromatically stained and sectioned at a thickness of 2 to 4 µm for effective visualization. Immunostains for myotilin and α-actinin all but clinch the diagnosis. However, nemaline rods may still be visible post-mortem in neurosarcoidosis, which may remain on the differential.[7] Generally the outcome is grim, with respiratory insufficiency the cause of death.

Treatment

Rehabilitation for muscle strengthening can be useful in alleviating symptoms.[8] Improvement has been noted in two HIV-negative individuals treated with immunoglobulin (IViG) agents.[9] Improvement has also been noted with autologous stem cell transplantation, and chemotherapy with melphalan.[10][11]

References
  1. Chahin N, Selcen D, Engel AG (October 2005). "Sporadic late onset nemaline myopathy". Neurology. 65 (8): 1158–64. doi:10.1212/01.wnl.0000180362.90078.dc. PMID 16148261. S2CID 23334154.
  2. Engel AG (November 1966). "Late-onset rod myopathy (a new syndrome?): light and electron microscopic observations in two cases". Mayo Clinic Proceedings. 41 (11): 713–41. PMID 5957590.
  3. Engel, W.K.; Resnick, J.S. (1966). "Late onset rod myopathy: a newly recognized, acquired, and progressive disease". Neurology. 16 (3): 308–9. doi:10.1212/wnl.16.3.299. S2CID 219213521.
  4. Engel WK, Oberc MA (March 1975). "Abundant nuclear rods in adult-onset rod disease". Journal of Neuropathology and Experimental Neurology. 34 (2): 119–32. doi:10.1097/00005072-197503000-00001. PMID 47386. S2CID 38570228.
  5. Suzuki M, Shimizu Y, Takeuchi M, Kobayashi M, Iwata M, Uchiyama S (February 2012). "Sporadic late-onset nemaline myopathy in a patient with primary Sjögren's syndrome". Journal of Neurology. 259 (2): 358–60. doi:10.1007/s00415-011-6160-4. PMID 21744311. S2CID 26449729.
  6. Keller CE, Hays AP, Rowland LP, Moghadaszadeh B, Beggs AH, Bhagat G (January 2006). "Adult-onset nemaline myopathy and monoclonal gammopathy". Archives of Neurology. 63 (1): 132–4. doi:10.1001/archneur.63.1.132. PMID 16401746.
  7. Bos MM, Overeem S, van Engelen BG, et al. (August 2006). "A case of neuromuscular mimicry". Neuromuscular Disorders. 16 (8): 510–3. doi:10.1016/j.nmd.2006.06.005. PMID 16919950. S2CID 12971698.
  8. Parks NE, Hanada EY (December 2012). "Maximizing functional independence in sporadic late onset nemaline myopathy". PM&R. 4 (12): 1020–3. doi:10.1016/j.pmrj.2012.06.008. PMID 23245665. S2CID 32083243.
  9. Milone M, Katz A, Amato AA, et al. (February 2010). "Sporadic late onset nemaline myopathy responsive to IVIg and immunotherapy". Muscle & Nerve. 41 (2): 272–6. doi:10.1002/mus.21504. PMID 19852026. S2CID 33462149.
  10. Hanisch F, Schneider I, Müller T, et al. (August 2013). "Behandelbarkeit der 'sporadic late onset nemaline myopathy'" [Treatability of sporadic late onset nemaline myopathy]. Der Nervenarzt (in German). 84 (8): 955–61. doi:10.1007/s00115-013-3825-5. PMID 23836301. S2CID 20819712.
  11. Novy J, Rosselet A, Spertini O, Lobrinus JA, Pabst T, Kuntzer T (February 2010). "Chemotherapy is successful in sporadic late onset nemaline myopathy (SLONM) with monoclonal gammopathy". Muscle & Nerve. 41 (2): 286–7. doi:10.1002/mus.21560. PMID 19918772. S2CID 36060636.
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