Thursday, November 27, 2014

Myotubular Myopathy

Definition

Myotubular myopathy is a congenital polymyopathy - a disease some people are born with that affects multiple muscles in the body.

Description

In these diseases, which are usually but not always recognized in infancy and early childhood, there is a structural abnormality of muscle from the time of embryogenesis (embryo production). Their identification has been made possible by the histochemical study of frozen (cryostat) sections of muscle biopsies and by electron microscopy.

The name myotubular myopathy comes from the appearance of affected muscle fibers that resemble myotubes, a type of fiber found only in fetal development. The disease is also called centronuclear myopathy because the nuclei of affected muscle cells are found in the center of the cell instead of at the periphery as is true with healthy muscle cells. The disease was first described in 1966.

In most instances, the affected infant shows less than the usual power of muscle contraction, hypotonia (floppiness and lack of resistance to passive movement of the limbs), and delay in the attainment of the milestones of motor development.

With growth, there is some improvement, but always a degree of muscular subnormality remains. In many cases, a slight increase in the motor deficit occurs later in life for unknown reasons.

The members of this group of relatively nonprogressive congenital myopathies are central-core myopathy, nemaline myopathy, the mitochondrial myopathies, myotubular myopathy, and other even rarer types (reducing body, fingerprint, zebra body, sarcotubular).

The course of the disease may or may not be progressive.

Causes

Myotubular myopathy occurs rarely. It is inherited as an autosomal (a chromosome other than a sex chromosome) dominant, recessive, or X-linked recessive trait.

Symptoms

Common symptoms of myotubular myopathy are drooping of the upper eyelids, facial weakness and foot drop, blackout spells, as well as some weakness of the limbs and trunk. People with the disease almost always lack reflexes in the affected muscles. The disease progresses slowly.

Treatment

There is no available treatment for these myopathies. However, providing orthosis for correction of skeletal deformities or even surgical correction often leads to improvement of functional disabilities.

Questions

Is the diagnosis of myotubular myopathy definitive?

How is it inherited?

How serious is the problem?

Is the condition progressive? Will it get worse?

What can be done to correct the symptoms?

Is surgery possible?

How can we best cope with the problem?