EDMD : EMERY-DRIEFUSS MUSCULAR DYSTROPHY

As I have discussed in brief about Neuromuscular disorders involving AHCs, Peripheral nerves, NMJs and Muscles in my earlier blog, in this one I would like to give an overview of such a disease involving muscles called Emery-Driefuss Muscular Dystrophy.

So Duchnne Muscular Dystrophy is the commonest type of muscular dystrophy known. In 1960s Prof. Alan Emery with his basic interest in DMD travelled to Virginia in order to identify genetic factors in the disease however it was necessary to study extensive families with several affected males. But such families were very rare because affected boys rarely survived beyond adolescence and therefore did not transmit the disease. He came across a scientific paper which published about an extensive family in Virginia affected with what the authors considered to be merely a mild form of Duchenne muscular dystrophy. Some of the affected males in the family had survived to middle age and had children. He wrote to the senior author of the paper, Dr. Fritz Dreifuss in Virginia, and was welcomed to see the family.

His first encounter was with a male in that family who was in his 50s and walked with a waddling gait. But apart from lordosis (exaggerated curve of lumbar spine) , he also walked with both elbows bent. He gave every appearance of a cowboy in a Western movie, who strolls out with both hands resting on his revolvers! He referred to this as the ‘cowboy gait’ and it seemed, to be unique to this disease.

After studying the family trees, blood samples and the laborious job of meticulous examination of each member of the family he came to a conclusion that it was clearly not Duchenne muscular dystrophy.

EDMD is distinguishable clinically from the Duchenne and Becker forms by absence of pseudohypertrophy of skeletal muscle, early involvement of the arms with elbow contractures, and early onset cardiac conduction abnormalities and atrial dysrhythmia. In EDMD serum creatine kinase (CK) level is normal or moderately increased, but in Duchenne muscular dystrophy, it can be 300 to 400 times greater than normal.

But it was not until 20 years after his first foray into the Appalachians that the reality of the disease as a distinct entity began to be accepted. This resulted from a scientific paper written by the eminent New York neurologist,Lewis Rowland,in 1979 in which he described a case and drew attention to the first description of the disease, and suggested the eponymous name Emery-Dreifuss muscular dystrophy.

The 3 genetic patterns of EDMD are: X-linked recessive fashion (the commonest form) produced by mutations in the emerin gene, which is located on the X-chromocsome (Xq28); autosomal dominant; and autosomal recessive. The 2 latter forms are caused by mutations in the lamin A/C gene on chromosome 1 (1q11–q23).

 

The classic triad of symptoms of EDMD are:

1.Early contractures, often before there is any significant weakness, of the elbows,Achilles tendons (the child typically begins walking on tiptoe) and postcervical muscles (with limitation of neck flexion but later forward flexion of the spine becomes limited);

2. Slowly progressive relatively mild muscle wasting and weakness with a humeroperoneal distribution (i.e., proximal in the upper limbs and distal in the lower limbs) early in the course of the disease. Later weakness also affects the proximal limb girdle musculature;

3.most importantly a cardiomyopathy usually presenting as cardiac conduction defects ranging from sinus bradycardia, prolongation of the PR interval to complete heart block.

In my current clinical practice recently I came across this young boy of 16 yrs of age affected with Emery-Driefuss Muscular Dystrophy. His chief complaints were walking on toes, slowly developing spinal deformity and fatigue which started to occur from the age of 6.

On examination he exhibited classical features of this disease in the form of Tightness of Tendo achillies along with bilateral elbow flexors, pectorals, shoulder abductors and flexors. He had grossly limited cervical spine flexion and exaggerated lumbar lordosis and a spinal scoliosis which was rigid and non- correctable in nature and a typical waddling gait.

On doing his PFT  (pulmonary function test) I found a very severe restriction in his lung capacities and his chest expansion parameters were also significantly reduced.

Note: The images have been removed due to privacy concerns.

Treatment:

It is primarily focused on the cardiac disease, with a pacemaker being the typical form of treatment. Bracing can also be helpful in some cases as the disease progresses. Unfortunately it was not advisable in this case because of his rigid deformity and restricted lung functions. Early, frequent range of motion exercises and positioning are also advisable and stretching exercises are indicated to minimize contractures. Genetic counselling plays a very important role.