Sensory processing disorder


Sensory processing disorder, formerly known as sensory integration dysfunction, is a condition in which multisensory input is not adequately processed in order to provide appropriate responses to the demands of the environment. Sensory processing disorder is present in many people with dyspraxia, autism spectrum disorder, Tourette's syndrome, and attention deficit hyperactivity disorder. Individuals with SPD may inadequately process visual, auditory, olfactory, gustatory, tactile, vestibular, proprioception, and interoception sensory stimuli.
Sensory integration was defined by occupational therapist Anna Jean Ayres in 1972 as "the neurological process that organizes sensation from one's own body and from the environment and makes it possible to use the body effectively within the environment". Sensory processing disorder has been characterized as the source of significant problems in organizing sensation coming from the body and the environment and is manifested by difficulties in the performance in one or more of the main areas of life: productivity, leisure and play or activities of daily living.
Sources debate whether SPD is an independent disorder or represents the observed symptoms of various other, more well-established, disorders. SPD is not included in the Diagnostic and Statistical Manual of Mental Disorders of the American Psychiatric Association, and the American Academy of Pediatrics has recommended in 2012 that pediatricians not use SPD as a stand-alone diagnosis.

Signs and symptoms

Sensory integration difficulties or sensory processing disorder are characterized by persistent challenges with neurological processing of sensory stimuli that interfere with a person's ability to participate in everyday life. Such challenges can appear in one or several sensory systems of the somatosensory system, vestibular system, proprioceptive system, interoceptive system, auditory system, visual system, olfactory system, and gustatory system.
While many people can present one or two symptoms, sensory processing disorder has to have a clear functional impact on the person's life.
Signs of over-responsivity, including, for example, dislike of textures such as those found in fabrics, foods, grooming products or other materials found in daily living, to which most people would not react, and serious discomfort, sickness or threat induced by normal sounds, lights, ambient temperature, movements, smells, tastes, or even inner sensations such as heartbeat.
Signs of under-responsivity, including sluggishness and lack of responsiveness.
Sensory cravings, including, for example, fidgeting, impulsiveness, or seeking or making loud, disturbing noises; and sensorimotor-based problems, including slow and uncoordinated movements or poor handwriting.
Sensory discrimination problems, which might manifest themselves in behaviors such as things constantly dropped.
Symptoms may vary according to the disorder's type and subtype present.

Relationship to other disorders

Sensory integration and processing difficulties can be a feature of a number of disorders, including anxiety problems, attention deficit hyperactivity disorder, food intolerances, behavioral disorders, and particularly, autism spectrum disorder. This pattern of comorbidities poses a significant challenge to those who claim that SPD is an identifiably specific disorder, rather than simply a term given to a set of symptoms common to other disorders.
Two studies have provided preliminary evidence suggesting that there may be measurable neurological differences between children diagnosed with SPD and control children classified as neurotypical or children diagnosed with autism. Despite this evidence, that SPD researchers have yet to agree on a proven, standardized diagnostic tool undermines researchers' ability to define the boundaries of the disorder and makes correlational studies, like those on structural brain abnormalities, less convincing.

Causes

The exact cause of SPD is not known. However, it is known that the midbrain and brainstem regions of the central nervous system are early centers in the processing pathway for multisensory integration; these brain regions are involved in processes including coordination, attention, arousal, and autonomic function. After sensory information passes through these centers, it is then routed to brain regions responsible for emotions, memory, and higher level cognitive functions.

Mechanism

Research in sensory processing in 2007 is focused on finding the genetic and neurological causes of SPD. Electroencephalography, measuring event-related potential, and magnetoencephalography are traditionally used to explore the causes behind the behaviors observed in SPD.
Differences in tactile and auditory over-responsivity show moderate genetic influences, with tactile over-responsivity demonstrating greater heritability. Differences in auditory latency, hypersensitivity to vibration in the Pacinian corpuscles receptor pathways, and other alterations in unimodal and multisensory processing have been detected in autism populations.
People with sensory processing deficits appear to have less sensory gating than typical subjects, and atypical neural integration of sensory input. In people with sensory over-responsivity, different neural generators activate, causing the automatic association of causally related sensory inputs that occurs at this early sensory-perceptual stage to not function properly. People with sensory over-responsivity might have increased D2 receptor in the striatum, related to aversion to tactile stimuli, and reduced habituation. In animal models, prenatal stress significantly increased tactile avoidance.
Recent research has also found an abnormal white matter microstructure in children with SPD, compared with typical children and those with other developmental disorders such as autism and ADHD.
One hypothesis is that multisensory stimulation may activate a higher-level system in the frontal cortex that involves attention and cognitive processing, rather than the automatic integration of multisensory stimuli observed in typically developing adults in the auditory cortex.

Diagnosis

Sensory processing disorder is accepted in the Diagnostic Classification of Mental Health and Developmental Disorders of Infancy and Early Childhood. It is not recognized as a mental disorder in medical manuals such as the ICD-10 or the DSM-5.
There is not a single test to diagnose sensory processing disorder. Diagnosis is primarily arrived at by the use of standardized tests, standardized questionnaires, expert observational scales, and free-play observation at an occupational therapy gym. Observation of functional activities might be carried at school and home as well.
Though diagnosis in most of the world is done by an occupational therapist, in some countries diagnosis is made by certified professionals, such as psychologists, learning specialists, physiotherapists and/or speech and language therapists. Some countries recommend to have a full psychological and neurological evaluation if symptoms are too severe.

Standardized tests

  • Sensory Integration and Praxis Test
  • Evaluation of Ayres' Sensory Integration – in development
  • DeGangi-Berk Test of Sensory Integration
  • Test of Sensory Functions in Infants

    Standardized questionnaires

  • Sensory Profile
  • Infant/Toddler Sensory Profile
  • Adolescent/Adult Sensory Profile
  • Sensory Profile School Companion
  • Indicators of Developmental Risk Signals
  • Sensory Processing Measure
  • Sensory Processing Measure Preschool

    Classification

Sensory integration and processing difficulties

Construct-related evidence relating to sensory integration and processing difficulties from Ayres' early research emerged from factor analysis of the earliest test the SCISIT and Mulligan's 1998 "Patterns of Sensory Integration Dysfunctions: A Confirmatory Factor Analysis". Sensory integration and processing patterns recognised in the research support a classification of difficulties related to:
  • Sensory registration and perception
  • Sensory reactivity
  • Praxis
  • Postural, ocular and bilateral integration

    Sensory processing disorder (SPD)

Proponents of a new nosology SPD have instead proposed three categories: sensory modulation disorder, sensory-based motor disorders and sensory discrimination disorders.

1. Sensory modulation disorder (SMD)

Sensory modulation refers to a complex central nervous system process by which neural messages that convey information about the intensity, frequency, duration, complexity, and novelty of sensory stimuli are adjusted.
SMD consists of three subtypes:
  1. Sensory over-responsivity.
  2. Sensory under-responsivity
  3. Sensory craving/seeking.

    2. Sensory-based motor disorder (SBMD)

According to proponents, sensory-based motor disorder shows motor output that is disorganized as a result of incorrect processing of sensory information affecting postural control challenges, resulting in postural disorder, or developmental coordination disorder.
The SBMD subtypes are:
  1. Dyspraxia
  2. Postural disorder

    3. Sensory discrimination disorder (SDD)

Sensory discrimination disorder involves the incorrect processing of sensory information. The SDD subtypes are:
  1. Visual
  2. Auditory
  3. Tactile
  4. Gustatory
  5. Olfactory
  6. Vestibular
  7. Proprioceptive
  8. Interoception.

    Treatment

Sensory integration therapy

Typically offered as part of occupational therapy, ASI that places a child in a room specifically designed to stimulate and challenge all of the senses to elicit functional adaptive responses. Occupational therapy is defined by the American Occupational Therapy Association as "Occupational therapy practitioners in pediatric settings work with children and their families, caregivers and teachers to promote participation in meaningful activities and occupations". In childhood, these occupations may include play, school and learning self-care tasks. An entry-level occupational therapist can provide treatment for sensory processing disorder; however, more advanced clinical training exists to target the underlying neuro-biological processes involved. Although Ayres initially developed her assessment tools and intervention methods to support children with sensory integration and processing challenges, the theory is relevant beyond childhood.
Sensory integration therapy is driven by four main principles:
  • Just right challenge
  • Adaptive response
  • Active engagement
  • Child directed
Serious questions have been raised as to the effectiveness of this therapy particularly in medical journals where the requirements for a treatment to be effective is much higher and developed than its occupational therapy counterparts which often advocate the effectiveness of the treatment.