DESTIN, FLA. – An increasing number of patients are presenting with muscular dystrophy in adulthood.
"We’re now finding more and more patients who are presenting with muscular dystrophy [and] becoming symptomatic in adulthood, not just at age 20, but even at age 30, 40, or 50 years old," Dr. Robert Wortmann said at the Congress of Clinical Rheumatology.
Dr. Robert Wortmann
In one case, a patient was diagnosed with a limb-girdle muscular dystrophy at 82 years of age, said Dr. Wortmann, professor of medicine at Dartmouth Medical School, Lebanon, N.H.
"So these are more common, more prevalent, and we’re learning a lot more about this disease," he added.
As an example, Dr. Wortmann presented one case involving a 20-year-old Brazilian exchange student with a 6-month history of progressive proximal muscle weakness. She had creatine phosphokinase (CPK) values that ranged between 20 and 60 times the upper limit of normal; a muscle biopsy showed lymphocytic inflammation. Corticosteroid and methotrexate treatment did not improve her condition.
She was found to have an autosomal recessive limb-girdle muscular dystrophy associated with dysferlin deficiency (limb-girdle muscular dystrophy type 2B, or LGMD2B). Dysferlin is one of the most common proteins to be deficient in this type of muscular dystrophy, Dr. Wortmann said.
Characteristics of LGMD2B include symmetric proximal myopathy, onset at 11-48 years of age (which has been expanded from an earlier identified range of late teens to early 20s), and very high CPK levels.
Caused by genetic defects in muscle cell proteins, muscular dystrophies are typically characterized by proximal muscle weakness, and later by muscle wasting. Early on in dystrophy, histology will look very similar to that of polymyositis.
"It may not be as profound a lymphocytic infiltrate, but it’s the same cells and the same distribution within the tissue," he said.
In fact, about 30% of cases in one series were first diagnosed with polymyositis, he said, noting that patients may even have some response to steroids.
Over time, however, this inflammation tends to decrease, and the muscle wastes and is replaced by fibrous tissue and fat," he said.
The muscle wasting represents an important distinction between polymyositis and muscular dystrophies, noted Dr. Wortmann.
The roles of various proteins in the associated genetic abnormalities continue to be defined, and limb-girdle muscular dystrophy is now considered to have 7 different autosomal dominant forms with different gene mutations, and 11 autosomal recessive forms that affect different structured proteins in the muscle and result in the identical presentation to polymyositis – including the LGMD2B disease identified in the case patient.
Not all patients with limb-girdle muscular dystrophy present with proximal myopathy, however.
In some cases, Miyoshi myopathy occurs, which is distal, late-onset myopathy. In other cases, there is mixed proximal and distal myopathy, he said.
"One thing I don’t understand – and I hope we learn some day why – is that some genetic disease that affects muscle will cause one phenotypic expression in one patient, and the same genetic defect in another patient will cause a different presentation," Dr. Wortmann said, adding that those that first appear to be polymyositis are generally the cases referred to rheumatologists and those with distal myopathy are generally those referred to neurologists.
Dr. Wortmann disclosed a financial relationship with Questcor.