What's your question? Ask

While the plant does, in fact, get its name from the sap containing oxalate crystals that can cause intense numbness and irritation if ingested, I don't think this should be an issue by simply touching it. That said, overly sensitive individuals could exhibit irritation so it's probably best to wear gloves when handling the plant. If you've already come into contact with its sap, wash your hands thoroughly and call a doctor if it worsens.

You can try to make sure the plant is receiving enough sunlight. The lower leaves are often shaded by the plant and don't receive enough light. They drop off and will not grow back.
If you plant is too tall, this could be a good time to start new plants with cuttings.
This article will help you.

https://www.gardeningknowhow.com/houseplants/dumb-cane/propagating-dieffenbachia.htm

Most dieffenbachias will grow from 3 to 6 feet tall and 1 to 3 feet wide.

These articles will help you identify the problem:

https://www.gardeningknowhow.com/plant-problems/environmental/what-causes-brown-edges-on-leaves-of-plant.htm
https://www.gardeningknowhow.com/houseplants/dumb-cane/growing-dumbcane-dieffenbachia.htm

Overwatering is very common in houseplants and less common in plants outdoors. If overwatering is a problem, your Dieffenbachia will show some of the symptoms in this article:

https://www.gardeningknowhow.com/plant-problems/environmental/signs-of-plants-affected-by-too-much-water.htm

Too much light can cause browning or whitening from sunburn on this plant species, but this is usually all over the leaf or scattered randomly across the leaf, not just on the edges.

Dieffenbachia can easily be damaged by low temperatures so that is most likely the cause. Move the plant indoors and put it in a place where it will get enough light, but not very bright light:
https://www.gardeningknowhow.com/houseplants/dumb-cane/growing-dumbcane-dieffenbachia.htm

The plant might grow more leaves by itself, but a better way to encourage it to grow more leaves is to cut the stem down to about 4 inches tall. HThis will encorage it to begin growing again.