Thread by @theneurolander

Myotonic disorders!

“after a fright, or in an unexpected joyous movement, this convulsive constriction occurs in all limbs…the victim can not stand upright”

Prussian physician Asmus Julius Thomas Thomsen (1815–1896)

#MedTwitter #neurotwitter #EndNeurophobia #tweetorials

1/

Definition

“difficulty in relaxation of a muscle after maximum voluntary contraction”

It can be specifically
- aggravated by conditions
- affecting regions of the body
- triggered

2/

Myotonic or Tennessee fainting goat

“important in history due to role of chloride channel in muscle excitation”

- 1880s, Marshall County
- CLCN1 gene

via: jimmywan87

3/

Classification of myotonic disorders

4/

Electrophysiology

Waxing & wanning of both amplitude & frequency
Potentials
- repetitive discharges
- 2 types: biphasic (<5ms) and positive waves (5-20ms)

5/

Dive-bomber

“High frequency discharges in EMG that vary in amplitude & frequency, waxing & waning continuously with firing frequencies ranging from 150/second down to 20/second and producing a sound that has been referred to as a dive bomber sound

*turn sound on

6/

Electrical myotonia differential

7/

Eyelid myotonia

“tries to open his eyes after having squeezed them tight”

- persist 1-2 minutes
- recruit additional muscles: frontalis

via: neurosigns.org

8/

Tongue myotonia

“tongue protrude, place a depressor on it, hit the tongue depressor with a reflex hammer”

- not clinically visible on inspection
- knot on the side of the tongue after percussion
(Handkerchief knot sign)

doi.org/10.1056/nejmic… VIA: NEJM

9/

Handgrip myotonia

“make a fist and then fully open the hand”

- open of the fist require other hand

doi.org/10.1056/nejmic… via: NEJM

10/

Handgrip myotonia

can also be noticed

“after a percussion of thenar eminence”

via: Fahad Hossain

11/

Warm-up phenomenon vs paramyotonia

Warm-up phenomenon
-repeated contraction improve myotonia
-usually, after 6 attempts

Paramyotonia (paradoxical myotonia)
-repeated contraction worse myotonia
-usually, in the eyes
-paramyotonia congenita & hyperkalemic periodic paralysis

12/

Lid lag myotonia

“delay btw eyeball movement and the upper eyelid movement when performing quick vertical eye movements”

-especially, looking up and asked to look rapidly downward, while head still & straight
-staring gaze for 1min

doi.org/10.1212/WNL.00… via: Neurology

13/

Tented Mouth

“triangular appearance of the oral aperture with the apex in the midpoint of the upper vermilion and the lower vermilion forming the base”

- congenital myotonic dystrophy

14/

Herculean appearance

- aka, bodybuilder-like appearance
- myotonia congenita

15/

Toe-extension myotonia

- DM1

DOI: doi.org/10.1212/WNL.00… via: Neurology

16/

Smooth muscle myotonia

- rare, in nondystrophic types

Can lead to
- dysphagia; esophagus
- abdominal pain & vomiting; GIT
- gallstones; delayed emptying gallbladder

Cesarean delivery recommended due to incoordinate contraction of uterus

17/

Myotonic dystrophies

DM 1
- CTG trinucleotide repeat on DMPK gene
- most common myotonic disorder

DM 2
- CCTG tetranucleotide repeat on CNBP gene
- rare disorder

18/

Myotonic dystrophy mnemonic
@medicowesome

19/

Non dystrophic myotonia

Channelopathies

20/

Non dystrophic myotonia - chloride channel
•No systemic effects, normal lifespan

Becker
- AR
- severe & progressive

Thomsen
- AD
- mild & nonprogressive

21/

Non dystrophic myotonia – sodium channel

3 types:
- potassium-sensitive
- paramyotonia
- hyperkalemic periodic paralysis

They are AD & caused by mutation in SCN4A gene

22/

Potassium-sensitive myotonia (potassium aggravated myotonia)

Exacerbated by potassium, but not to cold
3 variants
- fluctuans (intermittent related to exercise)
- permanens (constant w/ worsening periods)
- acetazolamide-responsive

23/

Paramyotonia congenita

Paradoxical myotonia
1st signs of stiffness as prolonged eye closure, after
- crying
- sleep near a fan
- washing face w/ cold water

24/

Hyperkalemic periodic paralysis

“early childhood w/ episodes of periodic weakness”

- attacks in the morning & fasting
- 3 variants: HyperKPP w/o myotonia; w/ myotonia; w/ paramyotnia

25/

Schwartz-Jampel syndrome (chondrodystrophic myotonia)

"prominent and diffuse myotonia that is present at birth"

26/

Electrodiagnostic tests

a.muscle cooling
AD myotonia congenita (MC), burst
PMC, silence➡️contracted

b.short exercise test
AD MC, drop w/ quick recover
AR MC, decremental
PMC, decremental w/ slow recover

c.prolong exercise test
AR, quick recover
HyperKPP, slow recover

27/

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Have a great day!