Muscle Biopsy - nemaline myopathy

ACEM

Nemaline myopathy

This condition belongs to the group of hereditary disorders known as congenital myopathies (congenital - present before, or at birth; myopathy - a disease of muscle). Congenital myopathies are distinguished from numerous other muscular disorders by the fact that they have a particular structural change in the skeletal muscle, which is detectable with the aid of the light microscope and can be confirmed with the electron microscope.

The symptoms

Nemaline myopathy is divided into three broad groups, although some overlap exists. Symptoms can appear at any age. In the severe neonatal onset group, infants are weak from birth, they have feeding, respiratory and cardiac problems that generally lead to death in the first weeks or months of life.

The most common form of nemaline myopathy is a mild non progressive, or slowly progressive, disorder of childhood. There may be symptoms present at birth but these are usually less marked than in the group described above. There is weakness in limb, trunk and facial muscles, the facial weakness affecting speech and swallowing. Many children remain active, but some develop skeletal abnormalities which exacerbate breathing difficulties. Heart problems are also associated with this condition.

Adult onset nemaline myopathy has a more varied group of symptoms and is usually progressive. In some cases early signs of the disorder are mild but progress to more severe disability later in life, in others, skeletal muscles produce no symptoms, and the condition is only detected when investigations for other problems are undertaken. In some instances muscle weakness may appear in patients who are in their thirties or forties without any preceding symptoms or without any family history of a similar condition.

Ultrastructural changes in nemaline myopathy

Nemaline comes from the Greek word nema meaning "threadlike", which was one of the descriptions given to the structures when first seen at the light microscope level.

In the low magnification image the fibrillar structure is disorganised and the thin dark bands (Z lines) are thickened. The thickened Z lines have formed nemaline rods, which, at higher magnification, can be seen to be a lattice like structure. nemaline rods at high power Nemaline rods can be seen from time to time in a number of conditions, and in both degenerating and regenerating muscle fibres, but when there is a clinical suspicion of nemaline myopathy, and no other significant pathological process is evident in the muscle (other than the presence of many nemaline rods) then the diagnosis of nemaline myopathy can be made.

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