Justwannadisappear, I don't know if this applies and your son's treatment team might already be using this technique, but I know that the children I work with who have severe emotional problems and also SPD get overwhelmed easily and lose their ability to communicate verbally. The children I work with are older than your son, but at times, they have tantrums that resemble a 3 yr. old tantrum. We use visual cue cards and sign to help them communicate easier when they are emotionally overwhelmed and can't "tell" us what they want or need. We introduce the use of cards and/or signs when they are calm and not overwhelmed. We practice the use of them so the aren't foreign when the meltdown actually ocurs.

For example, I worked with a girl who was fourteen who just totally disintergrated emotionally when frustrated or angry. She was able to come up with the one sign that was a signal that things were beginning to get out of control for her (two fists knuckle to knuckle--the sign for frustrated). We would practice this sign at different times when she wasn't actually frustrated so she became familiar and comfortable using it and knowing that staff understood and responded to her expression of frustration. She also carried a plastic sheet inside her notebook with things she could ask for to help her soothe when angry--pictorial respresentations of what she wanted to do to relieve her frustration. This is at a lot higher level than what a three year old can use or understand, but it gives you an idea how even an older child with SPD can learn to use supports to express their emotions when overwhelmed. I'm sure it's something your son's speech therapist could help you with. . . .of course, you all might already being doing something like this and the little guy is still struggling. I hope you and he are able to find a way to communicate in a more effective when when he's distressed. Take care.