39: Myotomic Muscle Disorders and Periodic Paralysis Syndromes

Question 1

How is myotonia characterized clinically?

Answer 1

Delayed muscle relaxation after contraction

Question 2

What myotonic disorders have dystrophic changes classically? No dystrophic changes?

Answer 2

Myotonic dystrophies;
myotonia congenita and paramyotonia congenita

Question 3

What is neuromyotonia associated with?

Answer 3

Peripheral nerve disorders

Question 4

How does muscle cooling affect myotonic disorders?

Answer 4

Can enhance myotonic discharges

Question 5

What conditions can lead to secondary hyperkalemic periodic paralysis?

Answer 5

Renal failure;
adrenal failure;
hypoaldosteronism;
metabolic acidosis

Question 6

What muscle disorders can be associated with myotonia?

Answer 6

Acid maltase deficiency, PM, myotubular and myofibrillar myopathy, malignant hyperpyrexia, drug-induced hypothyroidism

Question 7

Meds that can precipitate myotonia?

Answer 7

Clofibrate; propranolol;
terbutaline, colchicine, penicillamine;
cyclosporine, lipid-lowering agents

Question 8

Which chromosome and gene are affected with myotonic dystrophy type 1 and 2?

Answer 8

DMPK (protein kinase) gene, 19q;
CNBP (cellular nucleic acid-binding protein) gene, 3q

Question 9

What gene and chromosome are affected with myotonia congenita? What precipitates this, and what alleviates this?

Answer 9

CLCN gene, 7q for both AD and AR;
cold precipitates, exercise alleviates

Question 10

What do gene defects in SCN4A, chromosome 17q, lead to?

Answer 10

Sodium channel myotonia, paramyotonia congenita, hyperkalemic periodic paralysis

Question 11

What is affected in paramyotonia congenita? Is there periodic weakness? What precipitates and what alleviates?

Answer 11

Face, hands, thighs;
Yes;
Cold, exercise, and fasting;
warming

Question 12

What is affected in hyperkalemic periodic paralysis? Is there periodic weakness? What precipitates and what alleviates?

Answer 12

Generalized;
yes;
cold, rest after exercise, emotional stress, fasting, K loading;
carbs, mild exercise

Question 13

What gene defect is present with hypokalemic periodic paralysis? Periodic weakness? Provocative and alleviating factors?

Answer 13

CACNA1S gene, 1q (type 1), or SCN4A 17 q (type 2);
Yes;
Cold, rest after exercise, emotional stress, carbs, alcohol;
K, mild exercise

Question 14

What is myotonic dystrophy type 2 known as?

Answer 14

Proximal myotonic myopathy (PROMM)

Question 15

What is typical of the appearance of patients with myotonic dystrophy type 1?

Answer 15

Bifacial weakness, temporal wasting, frontal balding, ptosis

Question 16

What organs are involved in DM1?

Answer 16

Cataracts, cardiac conduction and pulmonary defects, endocrine dysfxn, testicular atrophy, gynecologic problems

Question 17

What is seen on muscle biopsy of DM1?

Answer 17

Mild increase in connective tissue, increased variation in fiber size, atrophy of type I muscle fibers, increase in central nuclei, ring fibers, and occasional small angulated fibers

Question 18

What determines clinical severity of DM1?

Answer 18

The number of CTG repeats

Question 19

What muscles are affected most in DM1 with regards to myotonic discharges?

Answer 19

Distal hand, forearm extensor, foot DF, facial muscles

Question 20

What is seen with DM1 with short exercise test?

Answer 20

Drop in CMAP amplitude immediately after exercise, but quick recovery over 2 mins

Question 21

What muscles are affected with DM2? What organ system tends to not be as involved compared to DM1?

Answer 21

Hip flexors and extensors, neck flexors, elbow extensors, finger and thumb flexors;
CNS involvement

Question 22

What is seen on biopsy with DM2?

Answer 22

Variation in fiber size, small angulated fibers, pyknotic nuclear clumps, predominant atrophy of type II muscle fibers, increased central nuclei

Question 23

AD myotonia congenita is known as? AR myotonia congenita is known as?

Answer 23

Thomsen; Becker

Question 24

What does muscle biopsy show with either AD or AR myotonia congenita?

Answer 24

Lack of type IIB fibers

Question 25

What is seen with the short exercise test with AD vs. AR myotonia congenita?

Answer 25

Variable drop in CMAP amplitude immediately after but recovers over 1-2 mins;
Large drop in amplitude with delay in recovery

Question 26

What brings on paramyotonia?

Answer 26

Repeated muscle contraction or exercise

Question 27

What is sodium channel myotonia congenita known as?

Answer 27

Potassium-aggravated myotonia

Question 28

What is seen with muscle cooling for paramyotonia? What does exercise test produce?

Answer 28

Transient dense fibs that disappear below 28 degrees C; the myotonic discharges disappear below 20 degrees, leading to paralysis;
large drop in CMAP amplitude with delay in recovery to baseline CMAP amplitude

Question 29

What test needs to be done for hyperkalemic periodic paralysis?

Answer 29

Prolonged exercise test (immediate increase in CMAP amplitude), but progressive drop in amplitude over 20-40 mins

Question 30

What does muscle biopsy show for hypokalemic periodic paralysis?

Answer 30

Vacuolar myopathy

Question 31

What is seen with hypokalemic periodic paralysis on prolonged exercise test?

Answer 31

Same as findings in hyperkalemic periodic paralysis

Question 32

What is the triad of Andersen-Tawil Syndrome? What gene is affected?

Answer 32

Periodic paralysis, cardiac abnormalities, facial and skeletal features;
KCNJ2 on chromosome 17q