DS3 -
At 4 years old, the probability is that you're not going to get a really solid diagnosis just yet. Not impossible - but unless its something really obvious (sometimes Autism Spectrum Disorders (ASD) stuff is really that obvious, but not always), dxes come in dribs and drabs and spurts.
Keep an open mind. Try approaches that are common for ADHD... but if they don't work well, also try approaches that work for Autism Spectrum Disorders (ASD). See for yourself what works, what doesn't. Start a journal, or a parent report, to capture what you've tried and with what results.
We'd have NEVER guessed Auditory Processing Disorders (APD) until much later. The Developmental Coordination Disorder (DCD)? saw that at 3 but didn't know what it was. Autism Spectrum Disorders (ASD) was on again/off again repeatedly - now its "off" - clinically significant findings (some traits) but doesn't meet diagnostic cutoff.
Just to really confuse you (just kidding)... many dxes that are stand-alone, are also traits of Autism Spectrum Disorders (ASD). ADHD, Developmental Coordination Disorder (DCD), Obsessive Compulsive Disorder (OCD), Sensory Integration Disorder (SID), just to name a few. A kid can be all of those and NOT be Autism Spectrum Disorders (ASD), or only have some traits of some of those (plus other stuff) and definitely be Autism Spectrum Disorders (ASD).
In other words... welcome to the journey of discovery!
(just wish the difficult children didn't drive us around the bend while we try to "get there")