Muscular dystrophies

 

Duchene MD 1/3300

Becker MD 1/18,000

Emery-Dreyfus MD 1/100,000

Myotonic dystrophy 1/8000

Oculopharngeal MD - common in Quebec (founder effect)

 

Hypertrophy - increased bulk of strong muscles

Pseudohypertrophy - increased bulk of weak muscles

 

- Check thigh abductors and glutei muscles

- Gower's maneuvre - classical of any proximal muscle weakness

- Normal CK doesn't rule out dystrophinopathy

 

DMD 60% deletions, 10% duplications, 30% likely point mutations.

 

Becker's starts around age 11. More likely cardiac involvement due to high activity level compared to DMD. Starts with LVH, then RVH and LVH.

 

For biopsy, use weak but not endstage muscle. Avoid injected muscles. Talk to pathologist.

 

Poor correlation between mutation and phenotype.

 

Management:

- diagnosis - be careful with pathology

- suveillance- CXR, ECK, CK

- anaesthesia risks - no O/P anaesthesia

- GI disturbance

- educational planning

- corticosteroids (Predisone/Deflazacort), side effects, monitoring

- PT

- weight management

- mechanical assistive devices

- orthopedics for posture

- monitoring of resp function

- family support

- genetic counselling (X-linked dystrophin gene)

 

Congenital muscular dystrophy

- high arch palate

- contractures at birth

- floppy from birth

- weakness stable over time

- Laminin 2 (merosin) mutations most common. Extracellullar matrix involvement. Also integrin and collagen VI (Ullrich CMD).

- elevated CK

- muscle biopsy active from birth

- white matter changes in CNS, but not mentally handicapped. Can have seizures.

- CNS involvement in Walker-Warburg, Muscle Eye Brain Disease, and Fukuyama MD.

- No definite treatments exist.

 

Limb-Girdle MD

- multiple forms

- no definite treatments

- same management as DMD

 

Congenital myotonic dystrophy

- shaking hand inadequate to screen mother

- percuss tongue and thenar eminence

- early baldness and cataracts on fam hx. Pregnancy issues - PTL, polyhydramnios, multiple miscarriages

- DMPK (myotonin-protein kinase) trinucleotide repeat

- RNA disease - transcription errors

- multisystem disorders

- ankle weakness, cardiac/resp disorders, somnolence, smooth muscle issues (swallowing, sphincter tone, gallstones), cataracts, endocrine disorders, cognition

- no role of steroids. Phenytoin can control myotonia if needed. Avoid anaesthesi.  Methylphenidate or Modafenil for somnolence.

- myotonia manifests by age 9-10