Clinical Summary

A 33-year-old female with past medical history of hypothyroidism presents with a 3-year history of insidious onset weakness in the ankles with recurrent falls. Later in the course she develops additional weakness in her hands. She begins requiring bilateral ankle-foot orthoses, experiencing difficulty with ambulating long distances, and performing any kind of dextrous movements with her hands. She does not report sensory changes. There is no family history of neuromuscular or inflammatory diseases. On physical examination, there is asymmetric muscle wasting involving the intrinsic hand and foot muscles and forearm musculature. She demonstrates bilateral steppage gait and cannot heel walk but is able to walk on her toes. She can perform a low squat with some difficulty. Her hands show weakness of finger abduction and flexion. Reflexes are intact. There are no fasciculations or spasticity. Electromyography demonstrates a combination of myopathic and neurogenic features.  MRI of the cervical and lumbar spine is normal. Laboratory investigations reveal a CK of 493, a medium positive result for anti-Ro52 antibodies, weak positive anti-PM/Scl 75, normal CRP, negative ANA and rheumatoid factor, negative serum electrophoresis, and non-reactive serology for Lyme, hepatitis B, C, HIV, and syphilis. All anti-ganglioside antibodies are negative. The patient is treated with monthly IVIG with no improvement in symptoms. A muscle biopsy is pursued for further evaluation.

Discussion points

1. What is the histopathologic differential diagnosis and what is the most likely clinicopathologic diagnosis?
2. What further stain can be pursued on the muscle biopsy to support the diagnosis?