Presentation: Adult with suspected myotonic dystrophy

A 40-year-old man attends clinic complaining of weakness in his hands. He has recently been diagnosed with atrial fibrillation. His father and brother have cataracts and diabetes. He has a myopathic face with bilateral ptosis and frontal balding. Electromyography demonstrates myotonia.

• Consider testing in anyone with myotonia, especially if there are additional features of myotonic dystrophy type 1. These can include:
  • myopathic face with ptosis, temporalis wasting and frontal balding;
  • early onset cataracts (‘Christmas tree’ cataracts are pathognomonic);
  • endocrine conditions such as diabetes mellitus or thyroid disease;
  • cardiac conduction disease, especially atrial flutter or fibrillation or ventricular tachycardia;
  • obstructive sleep apnoea and/or respiratory muscle weakness;
  • excessive daytime sleepiness;
  • learning disability or a neurodevelopmental condition; and
  • family history of sudden death.
• Unaffected individuals may present with a family history of an adult-onset genetic condition. Where signs and/or symptoms suggestive of that condition are not present in the patient, they should be offered referral to a local clinical genetics service to discuss testing as part of a predictive (presymptomatic) testing pathway.
• A genetic diagnosis may have implications for other family members, and can be particularly relevant during a pregnancy. For some genetic conditions, rapid testing is available for the purposes of pregnancy management. Assessment of symptoms during pregnancy and discussion of the patient’s choices regarding prenatal testing may be offered. If the patient or a close relative is pregnant, you may wish to offer them a referral to the local clinical genetics service for further discussion.

• Consult the National Genomic Test Directory. From here you can access the rare and inherited disease eligibility criteria document for information about individual tests and their associated eligibility criteria. You can also access a spreadsheet containing details of all available tests.
  • For information about how to arrange testing in Wales, Scotland or Northern Ireland, see our dedicated Knowledge Hub resource.
• To find out which genes are included on different gene panels, see the NHS Genomic Medicine Service (GMS) Signed Off Panels Resource.
• Decide which of the panels best suits the needs of your patient and/or their family.
  • R72 Myotonic dystrophy type 1: This panel looks for short tandem repeat (STR) expansions of the DMPK gene only.
  • R410 Myotonic dystrophy type 2: This panel should be used if there is clinical suspicion of myotonic dystrophy type 2 or if myotonic dystrophy type 1 has been excluded. It includes STR testing of the CNBP gene only.
• Myotonia can be seen in other genetic neuromuscular conditions without systemic features. Please see Patient with muscle cramps and myotonia.
• For tests that do not include whole genome sequencing, including R72 and R410:
  • you should use your local Genomic Laboratory Hub (GLH) test order and consent (record of discussion) forms; and
  • tests are DNA-based, and an EDTA sample (typically a purple-topped tube) is required.
• Information about patient eligibility and test indications were correct at the time of writing. When requesting a test, please refer to the National Genomic Test Directory to confirm the right test for your patient.

For clinicians

• GeneReviews: Myotonic dystrophy type 1
• NHS England: National Genomic Test Directory

References:

• Ashizawa T, Gagnon C, Groh WJ and others. ‘Consensus-based care recommendations for adults with myotonic dystrophy type 1’. Neurology Clinical Practice 2018: volume 8, issue 6, pages 507–520. DOI: 10.1212/CPJ.0000000000000531

For patients

• Myotonic Dystrophy Foundation
• Myotonic Dystrophy Support Group
• UK Myotonic Dystrophy Patient Registry