Jacqui,
Was PEPD considered as a diagnosis rather than EM? It's so similar, and involves the same SCN9A gene as inherited EM, but affects genitalia and rectum mostly rather than mostly hands,feet, ears and face like EM. Here's a couple of links that mention it affects the genital region. Some kids with it have seizures but some do not.
http://www.neurology.org/content/69/6/586.abstract
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2077381/
It's just a thought, in case that wasn't considered.