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Chapter 20: Neuromuscular Pathology

A 3-month-old infant, with poor muscle tone (hypotonia) and hepatomegaly, was not gaining weight as expected and was having difficulty in breathing. A heart murmur was also detected. Laboratory testing revealed an elevated CK, AST, and ALT. A muscle biopsy was recommended.

What would be the expected finding on muscle biopsy?

A. Vacuolated myocytes and increased glycogen on the PAS stain

B. Myocyte atrophy and inflammation on the H&E stain

C. Blue rod-like structures on the Gomori trichrome stain

D. Dystrophin stain showing almost complete absence of membrane staining

Answer: A

A 3-month-old infant, with poor muscle tone (hypotonia) and hepatomegaly, was not gaining weight as expected and was having difficulty in breathing. A heart murmur was also detected. Laboratory testing revealed an elevated CK, AST, and ALT. A muscle biopsy was recommended.

If the family wished to pursue a more definitive diagnosis with molecular genetic testing, what is the recommended test?

A. Array comparative genomic hybridization (CGH) for the DMD gene

B. GAA gene deletion/duplication analysis

C. SMN1 gene sequencing and dosage analysis

D. PYGM gene sequencing

Answer: B

Explanation for Questions 1 and 2: Pompe disease, also known as acid maltase deficiency or GSDII, is caused by glycogen accumulation due to a deficiency of the lysosomal acid alpha-glucosidase (GAA) enzyme. The accumulation damages organs and tissues throughout the body, particularly the muscles, but also the liver and heart.

It is an autosomal recessive disorder. Three types of disease have been described which differ in severity and the age at which they appear. The classic infantile form is rare, rapidly progressive, and fatal in untreated.

Although molecular testing may be performed, biochemical testing of GAA activity (either absent or reduced) is usually performed for a definitive diagnosis and may be confirmed with genetic testing.

Muscle biopsy in Pompe disease shows the presence of vacuoles that stain positively for glycogen.

A 10-year-old girl presents to her PCP with a rash and fever. The rash is bluish-purple in color with a patchy distribution but is notable on her swollen eyelids and knuckles. Her mother noticed that it was becoming more difficult for her to get into the car and to brush her hair. She denied any pain. Lab tests revealed a normal CK but elevated C-reactive protein and erythrocyte sedimentation rate.

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