Myoglobinuria—the presence in urine of a 17.8-kDa, red pigment, iron-protein compound called myoglobin—results from rhabdomyolysis, which is the acute breakdown or necrosis of skeletal muscle fibers whose contents (among them…
McArdle disease, an autosomal recessive myophosphorylase deficiency leading to glycolytic defects, is the common glycogen storage disease (GSD). Other glycolytic defects—phosphofructokinase, phosphoglycerate mutase, and lactic dehydrogenase deficiencies—produce similar clinical pictures….
Hypothyroid Myopathy. Most patients with myxedema (chronic hypothyroidism) complain of weakness; 25% have objective proximal muscle weakness. Myoedema, an electrically silent mounding of percussed muscle, occurs in one third of…
Hypokalemia-associated weakness does not usually become problematic until potassium levels fall toward and then below 1.5 mEq/L, with mild weakness, fatigue, and muscle cramping giving way to severe and generalized…
Serum creatine kinase (CK) is mildly to, at most, moderately elevated (<10 times normal). Electromyography (EMG) discloses fibrillation potentials and a mixed population of motor unit potentials (MUPs): low-amplitude myopathic…
Pathogenesis of Dermatomyositis. A striking feature observed in muscle biopsies taken from patients with DM is the presence of a diverse collection of cell types: CD4+ T lymphocytes, B lymphocytes,…
Because malignancy may be associated with PM (up to 10% of patients), and especially with DM (up to 25% of patients older than 40 years), screening for cancer (carcinomas of…
The prevalence of PM/DM is 1 per 100,000 adults, with a female to male ratio of 2 : 1; there is also a childhood form of dermatomyositis. Presenting symptoms include…
Both DM1 and DM2 are characterized by skeletal muscle weakness and myotonia with additional multisystem involvement. DM1 commonly presents in adolescence and early adult life, as well as a severe…
DM2 is caused by an expanded cytosine-cytosine-thymine-guanine (CCTG) tetranucleotide repeat expansion located in intron1 of the zinc-finger protein 9 gene (ZNF9 gene) on chromosome 3q21.3. On normal alleles, there are…
