Pediatric Myasthenia Diagnosis Can Be Challenging, Study Shows

September 17, 2013

By Anne Harding

NEW YORK (Reuters Health) Sep 17 - Pediatricians should have a high index of suspicion when evaluating patients for myasthenia, according to the authors of a new surveillance study.

"Despite pediatric myasthenia being a rare condition, the autoimmune form is a treatable condition," said lead author Dr. Juliana VanderPluym, a pediatric neurologist at the University of Alberta in Edmonton, Canada. "The diagnosis can be difficult because one of the features of myasthenia is that it is a fluctuating condition. It's a diagnosis that often has to be made over time with multiple visits with the patient."

Pediatric myasthenia, which may be acquired or genetic, is a group of conditions that affect the neuromuscular junction, Dr. VanderPluym and her team explain in Pediatrics, online September 9. The most common type is juvenile myasthenia gravis (JMG), which is characterized by fluctuating skeletal muscle weakness that improves with rest.

JMG occurs when patients make antibodies to neuromuscular junction proteins, most commonly the acetylcholine receptors. Other types include congenital myasthenic syndromes (CMS) and transient neonatal myasthenia gravis.

To better understand the incidence, clinical features, diagnosis and treatment of pediatric myasthenia, Dr. VanderPluym and her colleagues looked at data from the Canadian Pediatric Surveillance Program, which tracks low-frequency, high-impact conditions. Over a two-year period, 57 confirmed cases of pediatric myasthenia were reported, including 52 cases of JMG and five cases of CMS.

Thirty-four of the JMG cases presented with generalized symptoms, while 18 patients had ocular symptoms only. Most of the children in the generalized group were white, while Asian patients predominated in the ocular group. Age at symptom onset ranged from birth to 17 years, while the median was 10 years.

In both groups, ptosis was the most common symptom, with all patients in the ocular group and 82% of the generalized group presenting with this symptom. Other symptoms among the generalized group included chewing difficulty (65%) and fatigue (62%).

Eighteen percent of the patients with generalized JMG had respiratory distress, while 6% presented with respiratory failure.

Among generalized JMG patients, 67% tested positive for acetylcholine receptor antibodies, while 44% of the ocular JMG patients did.

Thirty-three of the patients with JMG were treated with pyridostigmine (treatment information was not available for the 34th patient), and all showed improvement. Most of the patients given steroids or intravenous immunoglobulin also improved. Treatment information was available for 17 of the patients with ocular JMG, all of whom received pyridostigmine; 88% improved.

The incidence and prevalence of myasthenia would likely be similar in other parts of the world, Dr. VanderPluym told Reuters Health, but with ocular JMG being more common among Asian populations than generalized JMG.

Clinicians should understand that patients who test negative for acetylcholine receptor antibodies may still have JMG, the researcher said. If their clinical suspicion remains high, she added, doctors should proceed with more complicated testing like the Tensilon test or neuroconduction studies.

Dr. VanderPluym said a future goal of her research will be to look at long-term outcomes of pediatric myasthenia patients. "It would be nice to have more natural history studies on how kids do over time," she said. "We do find in the pediatric population there are children that get better on their own, but there is a subset who continue through life having issues."

SOURCE: http://bit.ly/18WKTd6

Pediatrics 2013.

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