Get a diagnosis as early as possible as treatment needs to start from a very young age.
Follow these steps:
Make an appointment with a paediatrician you trust when your child is between 18 and 24 months old. Explain that your child might be suffering from SPD, and provide a list of examples of his/her behaviour as evidence. The paediatrician will most likely refer you to a neurodevelopmental paediatrician. Ask the paediatrician to help you make the appointment with this neurodevelopmental paediatrician, and obtain a letter from your paediatrician to take with you on your visit.
Once the neurodevelopmental paediatrian has examined your child, ask that a detailed report be provided to your paediatrician irrespective of whether the neurodevelopmental paediatrian gives you a detailed verbal explanation. Many paediatric neurologists (should a neurodevelopmental paediatrician not be available to you) tend to make a diagnosis at this stage, and it is usually that your child is borderline autistic (most children with autism have SPD, but not all children with SPD are autistic). My sense is that making a diagnosis at this stage, is premature.
Make another appointment with your paediatrician, so you can discuss the content of the neurodevelopmental paediatrian's report. During the appointment, ask your paediatrician to refer you to an occupational therapist (OT) who specialises in sensory integration (SI). Ask the paediatrician to help you make the appointment with this OT, and obtain a letter from your paediatrician to take with you on your visit. Take the neurodevelopmental paediatrian's report along too.
The OT will carefully evaluate your child and write a detailed report that should be returned to your paediatrician and to the neurodevelopmental paediatrian.
Once you and your paediatrician have both reports (neurodevelopmental paediatrician and OT) available to you, you are best equipped to decide whether you have a child with SPD.
At this point, if time and money allow, I would recommend your child with SPD visits an educational kinesiologist who will carefully assess the child's brain profile and help confirm the diagnosis. The educational kinesiologist’s report needs to be shared with your paediatrician, the neurodevelopmental paediatrician and the OT.