Fasciculations in Late-Onset Pompe Disease: A Sign of Motor Neuron Involvement?

Abstract

A 48-year-old Polish man was evaluated for difficulties in climbing stairs and holding his upper limbs above the head level, which started at the age of 30 and progressively worsened. He also complained of breathing difficulties while performing light physical activities. His medical history was otherwise unremarkable, and no other member of his family suffered from neurological diseases. Physical examination showed upper and lower limb proximal weakness, normal muscle tone, deep tendon reflexes, and plantar responses; sensory examination was normal. Creatine kinase level was three times above the normal value (596 UI/l; range, 30-170). Needle electromyography in the deltoid, biceps brachii, and quad-riceps showed a mixed pattern with early, myopathic recruitment (small-amplitude polyphasic motor unit potentials with interference reached for low effort), associated with rare high-amplitude motor unit potentials superimposed at maximal effort, fasciculations (high-amplitude triphasic spikes, firing inconstantly at approximately 1/second) and sporadic fibrillation potentials at rest. Motor and sensory nerve conduction studies in the upper and lower limbs were normal except for a slightly decreased amplitude of the sural nerve sensory action potential, which had a normal velocity. Mild respiratory failure with reduction of forced vital capacity at 50% of predicted value was documented by pulmonary function tests. To further address the differential diagnosis between a primary muscle disease, supported by the early full recruitment, and a lower motor neuron disorder, supported by the presence of signs compatible with denervation such as fibrillation and fasciculation potentials and Figure 1: Muscle MRI. (A) Axial T1-weighted sequences showing adductor longus (arrows) and semimembranosus (arrowhead) fatty replacement. (B) Axial short-tau-inversion-recovery (STIR) sequences showing muscle hyperintensity. Muscle pathology, 20 × magnification: (C) hematoxylin-eosin; (D) periodic acid-Schiff (PAS) staining; and (E) nonspecific esterase. Sample taken from fasciculating muscle shows the presence of many angulated fibers next to fibers bearing large cytoplasmic vacuoles full of PAS-positive material.