Enzymatic assay on
muscle biopsy was not performed due to shortage of tissue.
Muscle biopsy is crucial for differentiation; however, in the future, larger studies could prove whether using the HMGCR antibodies alone would be sufficient to make the diagnosis and implement the immunosuppressive or intravenous immunoglobulin therapy.
This case points out a novel pathological finding seen in YPS, tubular aggregates on
muscle biopsy. Other patients with YPS have previously had myopathic features described, but there is limited information regarding the muscle pathology.
During the discussion it was pointed out that we do need to have facilities for
muscle biopsy to diagnose and treat these rare diseases.
Since
muscle biopsy is less invasive for patients compared to endomyocardial biopsy, cardiologists need to consider it regardless of muscle weakness.
Diagnosis is based on the clinical history of subacute evolving muscle weakness and the presence of nemaline rods on
muscle biopsy. Myopathic EMG with fibrillation potentials and normal or low serum CK are also supportive of the diagnosis.
Diagnosis is made by estimating the acid alpha glucosidase activity in either skin biopsy (Fibroblasts),
muscle biopsy (Muscle cells) or in white blood cells.
In doubtful cases, a skin and
muscle biopsy together with an electromyography will set the diagnoses apart.
EMG studies may be normal in half of the patients or may show non-specific myopathic changes.3
Muscle biopsy may show variation in size of muscle fibers, mild focal necrosis and occasionally mild inflammatory infiltrates in contrast to polymyositis, in which inflammation, necrosis and regeneration predominates.3 Although EMG studies and
muscle biopsy may be helpful, clinical and biochemical response to thyroxine is the ultimate clue to diagnosis.
Andrew Engel, Professor of Neurology at the Mayo Clinic in Rochester, for his contribution of the
muscle biopsy pathology images.
Muscle Biopsy: A Practical Approach, 4th Edition (online access included)
An immediate vastus lateralis
muscle biopsy was performed.
