What Is SPD and How Does It Relate To Misophonia?

Would you explain the more recent conceptualization of Sensory Processing Disorder? 

In the 1980s, other scholars proposed that defensiveness exists in other sensory channels, and several other types of sensory defensiveness were labeled and described, including auditory (sounds), visual (sights), and olfactory (smell).  Because the protective and the discriminative tactile systems address only tactile defensiveness, and not defensiveness in the other sensory channels, the more recent scholars theorized that the amygdala is the filter, with the inhibitory fibers not overriding the excitatory fibers. The excitatory fibers are constantly firing, thereby letting in the unimportant information so a person is wired for fight, flight, or freeze. The sympathetic and the parasympathetic nervous systems are not balanced. These scholars suggested using activities that provide deep pressure and slow, linear movement to help the inhibitory fibers override the excitatory fibers.

Moving into the 21st century, Dr. Lucy Jane Miller coined the terms more commonly used today. Sensory Integration Disorder is now referred to as a Sensory Processing Disorder (SPD), which is an umbrella term with three primary diagnostic categories: (a) Sensory Modulation Disorder (SMD), (b) Sensory Discrimination Disorder (SDD), and Sensory-Based Motor Disorder (SBMD). Each diagnostic category has subtypes.

SMD has three subtypes: (a) Sensory Over-Responsivity (SOR), (b) Sensory Under-Responsivity (SUR), and sensory craving (SC). Persons can have SOR, SUR, and/or SC in one or more of the various sensory channels. Sensory channels include: auditory (sounds), visual (sights), tactile (touch), pain, olfactory (smells), gustatory (tastes), proprioception/vestibular (position/movement), air temperature (hot or cold), and interoception (e.g., hunger pangs). Persons with SOR perceive the input from one or more of the sensory channels as noxious, harmful, or threatening.  For example, a child with an auditory over-responsivity might cover his ears when someone whistles or jangles his keys. In contrast, persons with SUR barely perceive the input from one or more of the sensory channels. For example, a child with bumps and bruises might feel little pain. And a person with SC seeks input from one or more of the sensory channels. Examples include a child touching and/or smelling objects as he walks through a room, a child who seeks movement having difficulty sitting still, and a child who seeks proprioceptive input (pressure) intentionally bumping into things, including people.

SDD has six subtypes: (a) Auditory, (b) Visual, (c) Tactile, (d), Taste/Smell, (e) Position/Movement, and (f) Interoception

SBMD has two subtypes: Dyspraxia and Postural Disorder. Persons with dyspraxia (poor motor planning) have problems doing new or unfamiliar tasks such as learning to tie shoelaces. They do not learn to tie the shoelaces automatically (without thinking), and when they feel stressed, the task of tying is even more challenging. Postural disorders include poor balance and low muscle tone.

Do only children have Sensory Processing problems? 

Sensory processing disorders cannot be cured. Therefore, adults have sensory processing disorders. Many adults were not diagnosed as children, however.

Would you explain how SPD might relate to Misophonia sufferers? Is there a specific subtype that might overlap?

Misophonia and auditory over-responsivity might overlap. (Note: SPD is used interchangeably with the term auditory over-responsivity. To be in sync with others, I will use the term SPD when referring to a sensory modulation disorder, including auditory over-responsivity.)

Misophonia is a strong dislike or hatred of specific sounds. Persons with misophonia dislike, soft or loud repetitive sounds, especially sounds made by the mouth. Triggers include chomping food, slurping a drink, snapping gum, humming, and whistling. Other triggers include opening a bag of chips, cracking knuckles, and texting with the volume on. (Note: Sounds are not triggers when the person with misophonia makes them. Sounds are triggers when another person makes them.)

When exposed to a trigger, persons with misophonia feel anger, disgust, and hate. In contrast, persons with hyperacusis feel pain from loud and/or high-pitched sounds such as sirens and alarms, screeching breaks on subways or buses, silverware clanking against dishes, children’s screams, and clapping. Some loud, repetitive triggers overlap with the triggers for misophonia. For example, silverware clanking against dishes is listed as a trigger for each condition.

Persons with SPD dislike all of the above sounds. The emotional manifestations (anger, disgust, and hate) and the behaviors (fight, flight, or freeze) of persons with misophonia and SPD seem similar.

Some persons diagnosed with misophonia are reported to have visual sensitivities in addition to their auditory sensitivities. The term misokinesia has been used to mean a hatred of movement. Persons with misokinesia strongly dislike seeing movements such as someone twirling her hair around and around her finger, someone moving his leg up and down while sitting, and someone chewing food or gum with his open mouth.

Persons with SPD typically have problems in more than one sensory channel; therefore, over-responsiveness to inputs such as visual and tactile in addition to auditory over-responsivity suggest SPD. However, the auditory sensory channel might be the only sense affected in SPD. Therefore, the question of whether misophonia and SPD are linked needs to be investigated. Please bear in mind that the current lack of research does not rule out a potential link between these two conditions.

SPD is thought to be a neurodevelopmental condition, meaning that it a disorder within the brain that affects emotions, self-control, attention/memory, and learning throughout the lifespan. Research is ongoing; however, the neurobiological mechanisms and the implicated structures in the brain are not well documented. The etiologies (causes) are unknown, but a genetic vulnerability is possible in some persons with SPD. Fewer studies exist for misophonia. Whether this condition is neurological or learned from experiences is controversial. Research is needed to investigate the similarities and the differences between SPD and misophonia and to investigate the possible co-occurrence of these conditions.

The potential exists that some persons have been misdiagnosed, and an incorrect diagnosis could lead to the wrong treatments, which could worsen the symptoms. The causes of misophonia and SPD could be different. Causes guide treatments. Therefore, research to find the causes for misophonia and SPD is important.

By Susan Nesbit, OT

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