Pereskiopsis Pathology?

     I recently noticed one of my plants developed a strange condition, coupled with leaf loss and slow growth rate. This condition is characterized by black warty-like bumps up and down the stalk of the pereskiopsis.
     I have stated previously that I am confined to indoor cacti growing and reliant on artificial lighting..In addition to this I recently relocated and there was a brief period in which my collection was not exposed to light and had inadequate ventilation; it was shortly after this that I noticed this new condition.
     I have my pereskiopsis in trays packed pretty close (not as close as in my recent experiment), and what is strange is that the condition has not spread to the surrounding plants. Here are some pics of what I'm talking about:

 

    In the first picture you can see the overall condition, including the leaf-loss..The second is a closeup of the deformation and discoloration on the stem of the pereskiopsis. Honestly, I am not sure what this is... I am calling on any readers to share their experiences or knowledge.
     Thanks in advance..Comment and subscribe!