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Table of Contents    
LETTER TO EDITOR
Year : 2016  |  Volume : 64  |  Issue : 5  |  Page : 1051-1052

Myotonic dystrophy type 2 presenting as inflammatory myopathy


1 First Department of Neurology, University of Athens, Medical School, Aeginition Hospital; Department of Neurology, G. Gennimatas General Hospital of Athens, Athens, Greece
2 Department of Neurology, G. Gennimatas General Hospital of Athens, Athens, Greece
3 Department of Medical Genetics, Athens University, Aghia Sophia Children's Hospital, Athens, Greece
4 First Department of Neurology, University of Athens, Medical School, Aeginition Hospital, Athens, Greece

Date of Web Publication12-Sep-2016

Correspondence Address:
Constantinos Papadopoulos
First Department of Neurology, University of Athens, Medical School, Aeginition Hospital; Department of Neurology, G. Gennimatas General Hospital of Athens, Athens
Greece
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0028-3886.190276

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How to cite this article:
Papadopoulos C, Panagopoulos G, Kekou K, Fardis V, Kitsiou-Tzeli S, Papadimas GK. Myotonic dystrophy type 2 presenting as inflammatory myopathy. Neurol India 2016;64:1051-2

How to cite this URL:
Papadopoulos C, Panagopoulos G, Kekou K, Fardis V, Kitsiou-Tzeli S, Papadimas GK. Myotonic dystrophy type 2 presenting as inflammatory myopathy. Neurol India [serial online] 2016 [cited 2019 Nov 15];64:1051-2. Available from: http://www.neurologyindia.com/text.asp?2016/64/5/1051/190276




Sir,

Myotonic dystrophy type 2 (DM2) is an autosomal dominant disorder, caused by mutations in the ZNF9 gene, and is characterized by myotonia, cataract and slowly progressive proximal muscle weakness.[1] We report the case of a 71-year-old man presenting with rapidly progressive weakness and laboratory features suggestive of inflammatory myopathy, finally diagnosed with DM2 due to the muscle biopsy findings.

A 71-year-old man presented with a rapidly progressive proximal weakness leading to the use of a cane over a period of 6 months. There was no family history of muscle disease. His clinical examination revealed weakness of hip flexors, knee extensors, finger flexors and neck extensors. Creatine kinase levels were elevated (800 IU/L) and needle electromyography showed small amplitude polyphasic motor units, fibrillation potentials, positive sharp waves and pseudomyotonic discharges.

As the clinical history, distribution of weakness and laboratory features were suggestive of an inflammatory myopathy, he underwent an open vastus lateralis muscle biopsy. Histopathology revealed an increased fiber size variation, type 2 fiber atrophy and predominance, numerous fibers containing internal nuclei and atrophic fibers with pyknotic nucleic clumps [Figure 1]. These findings raised the suspicion of DM2, and genetic testing revealed a CCTG expansion on the ZNF9 gene.
Figure 1: Hematoxylin and eosin staining in skeletal muscle section from our patient, showing increased fiber size variation with a high percentage of fibers containing internal nuclei and atrophic fibers with pyknotic nucleic clumps

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DM2 is a clinically heterogenous disorder, caused by a CCTG-repeat expansion in intron 1 of the ZNF9 gene. Patients present with slowly progressive proximal weakness and usually retain their ability to walk life-long. They commonly have myotonia and prominent myalgia, whereas other features of the disease include cardiac conduction defects, posterior subcapsular cataract and endocrinal abnormalities.[1],[2] DM2 is underdiagnosed because of its large clinical variability ranging from prominent myalgia (that is frequently misdiagnosed as fibromyalgia), to slowly progressive proximal muscle weakness in elderly patients, (who are not referred for evaluation).[2] Electromyography may show non-specific irritative spontaneous activity, without myotonic discharges mimicking other neuromuscular disorders.[2],[3] As a result, some patients undergo a muscle biopsy. The histopathology in DM2 is characteristic, revealing groups of angulated fibers, central nuclei, increased myofiber size variation with predominant type 2 fiber atrophy and pyknotic nuclear clumps more prevalent in type 2 fibers.[3],[4] These changes are universal, irrespective of the clinical symptoms, signs or course of the disease.[4]

This case highlights the utility of muscle biopsy as a diagnostic tool in atypical DM2 cases either with no specific clinical and electromyographic signs or because of less pathognomonic phenotypes. The highly characteristic histopathologic findings can help clinicians choose suitable patients for further molecular genetic testing.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

1.
Turner C, Hilton-Jones D. The myotonic dystrophies: Diagnosis and management. J Neurol Neurosurg Psychiatry 2010;81:358-367.  Back to cited text no. 1
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2.
Udd B, Meola G, Krahe R, Thornton C, Ranum L, Day J, et al. Workshop report of the 115th ENMC workshop: DM2/PROMM and other myotonic dystrophies. 3rd Workshop, 14–16 February 2003, Naarden, The Netherlands. Neuromuscular Disorders 2003;13:589-596.  Back to cited text no. 2
    
3.
Hilbert JE, Ashizawa T, Day JW, Luebbe EA, Martensa WB, McDermott MP, et al. Diagnostic odyssey of patients with myotonic dystrophy. J Neurol 2013;260:2497-504.  Back to cited text no. 3
    
4.
Schoser BG, Schneider-Gold C, Kress W, Goebel HH, Reilich P, Koch MC, et al. Muscle pathology in 57 patients with myotonic dystrophy type 2. Muscle Nerve 2004;29:275-81.  Back to cited text no. 4
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