39: Myotomic Muscle Disorders and Periodic Paralysis Syndromes Flashcards
How is myotonia characterized clinically?
Delayed muscle relaxation after contraction
What myotonic disorders have dystrophic changes classically? No dystrophic changes?
Myotonic dystrophies;
myotonia congenita and paramyotonia congenita
What is neuromyotonia associated with?
Peripheral nerve disorders
How does muscle cooling affect myotonic disorders?
Can enhance myotonic discharges
What conditions can lead to secondary hyperkalemic periodic paralysis?
Renal failure;
adrenal failure;
hypoaldosteronism;
metabolic acidosis
What muscle disorders can be associated with myotonia?
Acid maltase deficiency, PM, myotubular and myofibrillar myopathy, malignant hyperpyrexia, drug-induced hypothyroidism
Meds that can precipitate myotonia?
Clofibrate; propranolol;
terbutaline, colchicine, penicillamine;
cyclosporine, lipid-lowering agents
Which chromosome and gene are affected with myotonic dystrophy type 1 and 2?
DMPK (protein kinase) gene, 19q;
CNBP (cellular nucleic acid-binding protein) gene, 3q
What gene and chromosome are affected with myotonia congenita? What precipitates this, and what alleviates this?
CLCN gene, 7q for both AD and AR;
cold precipitates, exercise alleviates
What do gene defects in SCN4A, chromosome 17q, lead to?
Sodium channel myotonia, paramyotonia congenita, hyperkalemic periodic paralysis
What is affected in paramyotonia congenita? Is there periodic weakness? What precipitates and what alleviates?
Face, hands, thighs;
Yes;
Cold, exercise, and fasting;
warming
What is affected in hyperkalemic periodic paralysis? Is there periodic weakness? What precipitates and what alleviates?
Generalized;
yes;
cold, rest after exercise, emotional stress, fasting, K loading;
carbs, mild exercise
What gene defect is present with hypokalemic periodic paralysis? Periodic weakness? Provocative and alleviating factors?
CACNA1S gene, 1q (type 1), or SCN4A 17 q (type 2);
Yes;
Cold, rest after exercise, emotional stress, carbs, alcohol;
K, mild exercise
What is myotonic dystrophy type 2 known as?
Proximal myotonic myopathy (PROMM)
What is typical of the appearance of patients with myotonic dystrophy type 1?
Bifacial weakness, temporal wasting, frontal balding, ptosis
What organs are involved in DM1?
Cataracts, cardiac conduction and pulmonary defects, endocrine dysfxn, testicular atrophy, gynecologic problems
What is seen on muscle biopsy of DM1?
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
What determines clinical severity of DM1?
The number of CTG repeats
What muscles are affected most in DM1 with regards to myotonic discharges?
Distal hand, forearm extensor, foot DF, facial muscles
What is seen with DM1 with short exercise test?
Drop in CMAP amplitude immediately after exercise, but quick recovery over 2 mins
What muscles are affected with DM2? What organ system tends to not be as involved compared to DM1?
Hip flexors and extensors, neck flexors, elbow extensors, finger and thumb flexors;
CNS involvement
What is seen on biopsy with DM2?
Variation in fiber size, small angulated fibers, pyknotic nuclear clumps, predominant atrophy of type II muscle fibers, increased central nuclei
AD myotonia congenita is known as? AR myotonia congenita is known as?
Thomsen; Becker
What does muscle biopsy show with either AD or AR myotonia congenita?
Lack of type IIB fibers
