Effects of Phase Polarity and Charge Balance Spinal Cord Stimulation on Behavior and Gene Expression in a Rat Model of Neuropathic Pain.

OBJECTIVE: To investigate the effect of phase polarity and charge balance of spinal cord stimulation (SCS) waveforms on pain behavior and gene expression in a neuropathic pain rodent model. We hypothesized that differing waveforms will result in diverse behavioral and transcriptomics expression due to unique mechanisms of action. MATERIALS AND METHODS: Rats were implanted with a four-contact cylindrical mini-lead and randomly assigned to two control (no-pain and pain model) and five test groups featuring monophasic, as well as charge-unbalanced and charge-balanced biphasic SCS waveforms. Mechanical and cold allodynia were assessed to measure efficacy. The ipsilateral dorsal quadrant of spinal cord adjacent to the lead was harvested post-stimulation and processed to determine gene expression via real-time reverse-transcriptase polymerase chain reaction (RT-PCR). Gene expression, SCS intensity (mA), and behavioral score as percent of baseline (BSPB) were statistically analyzed and used to generate correlograms using R-Studio. Statistical analysis was performed using SPSS22.0, and p < 0.05 was considered significant. RESULTS: As expected, BSPB was significantly lower for the pain model group compared to the no-pain group. BSPB was significantly improved post-stim compared to pre-stim using cathodic, anodic, symmetric biphasic, or asymmetric biphasic 1:2 waveforms; however, BSPB was not restored to Sham levels. RT-PCR analysis showed that eight genes demonstrated a significant difference between the pain model and SCS waveforms and between waveforms. Correlograms reveal a linear correlation between regulation of expression of a given gene in relation to mA, BSPB, or other genes. CONCLUSIONS: Our results exhibit that specific SCS waveforms differentially modulate several key transcriptional pathways that are relevant in chronic pain conditions. These results have significant implications for SCS: whether to move beyond traditional paradigm of neuronal activation to focus also on modulating immune-driven processes.

Corneal Myxoma.

A 56-year-old woman referred to the ophthalmic service for evaluation of a lesion on her right cornea. There was no history of trauma or infection to the eye and there was no history of previous eye surgery or topical medications to the eye. Ophthalmic examination revealed a raised lesion with gelatinous appearance present at the nasal corneal limbus. Histologically, the corneal stroma was replaced by a myxoid matrix with scattered elongated spindle cells with no atypia consistent with corneal myxoma. Due to the rarity of the disease, our case highlights the importance of recognizing this entity. The treatment of choice is local excision.