Your son or daughter fidgets. They're fussy. They don't behave, and they play roughly with others. It's like they don't listen to you. They're easily distracted.
You wonder: Does my child have ADHD? Perhaps not. What you're seeing might be sensory processing disorder, or SPD, instead. It's important to know that unlike ADHD, SPD isn't in the book that psychiatrists use to classify mental health problems (the DSM-5) or the coding used to classify diseases (the ICD-10), so you can't be "diagnosed" with it. But understanding what's going on will give you and your doctor a better idea of how to help your child.
Both disorders will make you restless and unable to concentrate. You could also find it hard to control your emotions. Children might have frequent meltdowns. They're anxious and may act out in social settings.
SPD is when the brain doesn't correctly deal with the information coming in from the body's senses. "Normal" can hurt or overwhelm someone with SPD. A clothing tag touching them might cause them to cry out in pain. They may shield their eyes when you turn on a light. The texture and taste of food could be a big deal. Going to a restaurant can be a nightmare for them.
But others can have the opposite problem -- not enough input. They may have a high threshold for pain and won't realize they're in a dangerous situation, such as getting too close to a stove burner. They may want to touch, even when it's not appropriate, or they may seem clumsy or loud.
On the other hand, ADHD is more about focus and controlling impulsive behaviors. A child with ADHD may have learning issues or be gifted. They can't sit still and may always be "on the go." They might daydream a lot, forget or lose things, and talk too much.
Figuring out whether your child has ADHD or SPD is often difficult because, according to one study, 40% of children who showed symptoms of either ADHD or SPD had symptoms of both. Kids with SPD may adopt behaviors that look like ADHD to try to protect themselves or to feel better.
Talk to your pediatrician about what your child does, when it started, when it tends to happen, and if there's anything you can do that helps. They may want your child to see a specialist.
Drugs, such as amphetamine-based stimulants (Adderall, Adderall XR, etc) and methylphenidate-based stimulants (Concerta, Ritalin, etc) allow kids with ADHD to focus and not to act out in social situations. They may work to lessen impulsiveness for kids with SPD but sometimes they may cause kids to focus on the sensory inputs that overwhelm them.
Therapy and coaching can also help kids with ADHD become more organized and manage their time better. Sometimes, parents get training, too.
Treatment for SPD may include occupational therapies that can help a child get used to sensory stimulation. This could include activities like jumping into a ball pit, walking barefoot, or crashing into a padded wall.