Late Onset Pompe Disease Under the Mask of Myoclonus Epilepsy

Introduction: Practicing physicians are unfamiliar with the manifestations of Pompe disease, in particular with the clinical variability of its late-onset form. To illustrate this, we will describe an unusual case that occurred in 2006. Case Description: A 16 year old boy diagnosed with myoclonic epilepsy was admitted to our clinic. Till the age of 14 years, he appeared healthy until generalized jerks started to occur twice a day. In six months time, the frequency increased to 10 times a day. He was administered valproate in daily doses of 20 mg/kg and the jerks disappeared, but generalized spike waves persisted on the electroencephalogram. An increase in the daily dose of valproate to 37 mg/kg had no effect. At the age of 15, tonoclonic seizures started. Topamax was added at a daily dose of 200 mg without effect. Then, Topamax was replaced by Keppra (daily dose – 20 mg/kg) with short-term effect. Along with ongoing valproate administration, the daily Keppra dosage was increased to 60 mg/kg but this had no effect. The occurrence of confusion and slow waves were considered to be valproic encephalopathy symptoms. In our clinic, we performed muscle biopsy to rule out MERRF syndrome. Light microscopic studies (including a histochemical study) of the biopsy material have not revealed any blatant changes. Subsequent electron microscopy did reveal intralysosomal storages of glycogen. The pathologist considered it to be proof of glycogenosis II. However, the clinicians disagreed because of the intensity of epilepsy symptoms, despite moderate increase of creatine phosphokinase (262 E/l), aspartate (62 ME/l) and alanine (91 ME/l) aminotransferases, myocardium repolarization disturbance and moderate hepatomegaly. The boy was discharged with complementary antiepileptic treatment prescription, without investigation of acid -glycosidase activity. A month later he died of epileptic status in a local emergency hospital. Conclusion: Although we have not obtained enzymatic and molecular genetic evidence, the fast disease progression, specific electron microscopic observations, the above-mentioned biochemical data, myocardial changes and hepatomegaly support the diagnosis of late-onset acid -glycosidase deficiency. In this case, the disease clinically resented as myoclonic epilepsy.