Objective:

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Background:

Late-Onset Pompe Disease (LOPD) is a rare adult glycogen storage disease of important diagnostic significance in light of potential enzyme replacement therapy (ERT). We highlight here a case where anchoring bias resulted in misdiagnosis of radiation myositis and plexopathy, delaying the correct diagnosis of LOPD to the patient’s detriment.  

Design/Methods:

A 64-year-old woman presented to neuromuscular clinic for evaluation of 17 years of slowly progressive bilateral lower limb weakness. She had a history of remote endocervical carcinoma treated prior to onset of weakness with hysterectomy, extensive lymph node dissection, and pelvic radiation. Neurologic examination revealed bilateral hip flexor, abductor, and adductor weakness, right worse than left with normal sensation and absent lower extremity reflexes. Prior nerve conduction study (NCS) showed reduced proximal lower extremity motor amplitudes with normal distal motor amplitudes and normal sensory NCS. Needle electromyography (EMG) showed fibrillation potentials and myotonia in the lower extremity with polyphasia, but was ultimately aborted, due to patient discomfort.  MRI of the pelvis demonstrated symmetric bilateral atrophy and T2 hyperintensity in the obturators and adductors, and severe fatty infiltration of the glutei and hamstrings with otherwise normal musculature. She carried a diagnosis of mixed radiation plexitis and myositis for several years until she was evaluated in neuromuscular clinic where Pompe enzyme activity was tested in the serum resulting a diagnosis of LOPD and initiation of ERT. 

Results:

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Conclusions:

Discussion: Normal distal sensory nerve conductions and MRI pattern were most consistent with an inherited myopathy. Anchoring bias given substantial history of pelvic malignancy and radiation resulted in minimization of the significance of these findings. Consideration of treatable hereditary disorders despite their rarity, is of importance to reduce treatment delay.