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BACKGROUND AND CLINICAL INFORMATION: Head

Summary: First recognized by Brooke in 1973. This is a congenital myopathy with characterized by hypotonia can be recognized at or shortly after birth and the degree of weakness varies considerably. Muscle of both the trunk and extremities are involved although those of the legs may be more severely affected. Respiratory insufficiency is common during the early stages of life. The disease becomes static or improves as the child grows. The pattern of inheritance is not clear but probably autosomal recessive or autosomal dominant. Histologically, there is characteristic reduction in caliber of all or most type 1 muscle fibers.

Genetics: Unclear but is probably autosomal recessive. Occasional families suggest autosomal dominant transmission.

Clinical:

· Floppy infant: The floppyness is usually recognized at the time of birth or shortly after birth. Muscle weakness is disproportionately less than hypotonia, and tendon jerks are often absent.

· Course of disease: Although some cases may have initial progression of disease but no disease progress should be seen in any patient older than 2 years of age. In contrast toe Werdnig-Hoffman’s disease, congenital fiber type disproportion tends to become static or may improve as the child grows.

· Extent and severity: Muscle of both extremities and trunk are involved but the legs seem to be more involved than the arms. The degree of weakness is highly variable. In severe cases, voluntary movement of extremities is not seen until two years of age; in cases with mild involvement, only some developmental delay is seen. Some may never become functionally disabled and may not seek medical advice.

· Respiratory failure: is common during the first year of life.

· Abnormal statute: Most patients are below 3 percentile of weight even with normal birth weight and 10 percentile of height.

· Other malformations and deformities: High arched palate, kyphoscoliosis, deformities of the feet.

· EMG and serum CK: Mild increase in serum CK in a few patients and the EMG gives a myopathic pattern.

· Clinical differential diagnosis: Werdnig Hoffmann’s disease, demyelinating diseases involving peripheral nerves.

HISTOPATHOLOGY AND IMMUNOHISTOCHEMISTRY: Head

Type 1 fiber:

· Histology: There is moderate to marked reduction in the caliber of all or most type 1 fibers but, unlike denervtion atrophy, their cross-sectional outline remains polygonal. There may be a relative increase in the number of type 1 fibers. Clustering of the small-caliber type 1 fibers is noted in many cases.

· Semithin: The number of capillaries is considerably reduced. Disturbed sarcomere organization may be present in some cases.

· EM: The large fibers are normal. The myofibrils in the small fibers tend to be irregular in size and shape. The Z-disc tends to be slightly zigzag. Small rings and even nemaline bodies may be present.

Type 2 fibers: They may be hypertrophic.

DIFFERENTIAL DIAGNOSIS: Head

Demyelinating disease involving peripheral nerves can cause muscle changes histologically similar to congenital fiber disproportion when biopsy is done in early childhood. This condition has been described in Krabbe’s disease and other types of central and peripheral demyelination, and other demyelinating diseases.

Other myopathies can also have small type I fibers and normal sized or enlarged type II fibers. These entities include neurogenic changes (atrophy), spinal muscular dystrophy, myotonic dystrophy, nemaline myopathy.