Module 5: Co-morbidities and why it is frequently misdiagnosed

There are several conditions for which SPD is very commonly also present. When two conditions are found to be co-occurring in the same individual, these are called co-morbidities. It means that if someone has one of a group of conditions, they are highly likely to also be diagnosed with one or more within the same group.

However, many people only have one diagnosable condition from these groups. Some will be discussed in more detail. SPD symptoms that are causing a high enough level of concern to merit a GP or other healthcare professional making a specialist referral may also indicate that co-morbid conditions may be present.

A lot of the SPD symptoms can look like ADHD and there is a considerable crossover of symptoms between SPD and autism, as well as each of the other conditions within this group of co-morbidities. This makes it highly likely that a child will be referred for a diagnostic assessment of another named condition, rather than the referral being made on the strength of the SPD symptoms alone. With SPD, there are several potential co-morbidities, including:

• Seizures / epilepsy
• Autism
• Intellectual disability
• ADHD (attention deficit hyperactivity disorder)
• ADD (attention deficit disorder)
• Bipolar disorder
• Obsessive compulsive disorder
• Tourette’s syndrome
• General anxiety disorder
• Clinical depression
• Visual disorders
• Auditory disorders

5.1 SPD vs Autism Spectrum Disorder

Since children who are diagnosed with Autism Spectrum Disorder (ASD) often show sensory processing symptoms; the two are often mistaken for each other.  It is important to remember that while three-quarters of children with ASD have corresponding sensory symptoms, “most children with SPD do not have Autism Spectrum Disorder.” (Star Institute for Sensory Processing).

Researchers at University of California and San Francisco also found that children with ASD and SPD both have decreased structural brain connections, but each one affects different regions of the brain. This suggests that while autism and sensory processing disorder are often confused as one in the same, they have brain wiring differences.

The biggest difference between ASD and SPD is that those with ASD often present with considerable difficulties in social skills and language. While those with SPD can also have these same difficulties, the causes are not the same. ASD is typically brain based (neurological) while SPD is sensory based (modulation and discrimination).

Globally, it’s estimated that approximately 1 in 100 children have autism. However, this figure is an average, and reported prevalence can vary significantly between studies, with some well-controlled studies reporting higher numbers. In 2025, the Centers for Disease Control and Prevention (CDC) estimates that one in 36 children will be diagnosed with autism spectrum disorder (ASD).

Worldwide, autism is generally estimated to be diagnosed in boys about four times more often than in girls. However, it’s important to note that many autistic girls and women may not receive a diagnosis until later in life, if at all, according to Healthline. Some research suggests the male-to-female ratio may be as high as 5.5:1. 

Although ASD can be diagnosed as early as 2 years old, most children are around 4 years old when diagnosed. Most parents of children with autism report that they started noticing developmental problems around their child’s first birthday, or that previously reached developmental milestones seemed to “disappear”, which usually presented as a loss in expressive (spoken) language.  Autism is usually diagnosed by a team of specialists including a neurologist, neurophysiologist, or developmental paediatrician. SPD is typically evaluated and assessed by an OT.

5.2 SPD vs Attention Deficit Hyperactivity Disorder

Children who have a diagnosis of Attention-Deficit Hyperactivity Disorder (ADHD), are more likely to also have sensory processing difficulty or SPD. 

ADHD is a neurological condition that results from a chemical imbalance in the brain, that makes it very difficult for children to concentrate and focus. It affects their self-control, the ability to focus, organize, use working memory, and many other executive function skills, which are higher level critical thinking skills in the brain.

There is no single test that can be used to diagnose ADHD, much like SPD. Often a physician or specialist will interview the parents and ask a series of questions to figure out if certain behaviours have been happening on a regular basis for more than 6 months along with evaluating other criteria that needs to be met before a formal diagnosis can be given. ADHD is a recognized diagnosis in the Diagnostic and Statistical Manual of Mental Disorders (or DSM-5).

SPD is a response or non-response to incoming sensory stimuli. The cause of SPD is largely unknown, though there may be biological differences in the brain. ADHD and SPD do overlap and often may be confused. Some experts argue that ADHD is often misdiagnosed, when it is actually a sensory processing disorder, learning disability, anxiety or depression that is causing the inability to focus. 

5.3 What can put a child at higher risk of developing SPD?

• a stressful pregnancy
• a difficult delivery
• prenatal exposure to drugs or alcohol
• prematurity (which is more likely in younger mothers and with prenatal exposure to drugs or alcohol)
• maternal malnutrition
• being institutionalized or under-stimulated during critical periods of development (in simple terms, time spent in an orphanage or a long hospital stay)
• having Autism
• not receiving proper stimulation or enough stimulation to the senses during development
• having Foetal Alcohol Spectrum Disorder (FASD), ADD or ADHD, Fragile X or Down’s Syndrome
• other factors such as family history

Thus, we can see from list that adopted children who underwent trauma and was maybe institutionalised is at greater risk of developing SPD.