by Ahmad Ghanizadeh, MD
Associate Professor of Child and Adolescent Psychiatry, Department of Psychiatry, Shiraz University of Medical Sciences, Hafez Hospital, Shiraz, Iran

Psychiatry (Edgemont) 2009;6(12):40–43


There was no funding for the development and writing of this article.

Financial disclosure

The authors have no conflicts of interest relevant to the content of this article.

Key Words

Sensory, ADHD, methylphenidate, nail, lip, autism, attention deficit hyperactivity disorder


Sensory processing problems in children with attention deficit hyperactivity disorder have been the focus of many studies in recent years. It is obvious that different aspects of sensory problems such as with tactile sensory are involved in attention deficit hyperactivity disorder. However, whether the sensory information process problems can be factors in decision making regarding pharmacological management of children with attention deficit hyperactivity disorder has not been researched. This case report presents two children with attention deficit hyperactivity disorder. The mother of the first patient reported that her child’s ability for detecting, identifying, and discriminating smells was very high and more than the other children at this age. As she reported, the child also liked to touch everything and everybody. He experienced nail biting after taking 20mg methylphenidate in single dosage. By decreasing of the dosage, nail biting disappeared in the three trials. The other patient started lip biting about half an hour after taking the first dosage of the medication. It continued for four hours. This report suggests that there is an association between methylphenidate and tactile sensory problems in children with attention deficit hyperactivity disorder.  It is possible that methylphenidate induces or exacerbates tactile hyposensitivity. If this assumption is supported in controlled clinical trials, then tactile sensory assessment might help to make decisions for the pharmacological management of children with attention deficit hyperactivity disorder. Further studies should investigate whether attention deficit hyperactivity disorder with sensory processing problems is a phenotype with an overlap between autistic disorders and attention deficit hyperactivity disorder in which stimulants may exacerbate some sensory processing problems. Also, if this is the case, the diagnosis of attention deficit hyperactivity disorder as an exclusionary criterion for pervasive developmental disorder needs to be revised.


Sensory processing problem is the exaggerated (avoidant and defensive) or inappropriate response to benign sensory input.[1] Many children with attention deficit hyperactivity disorder (ADHD) suffer from sensory information processing problems.[2] This sensory problem is seen in different aspects of sensory processing, such as auditory,[3] olfactory, and tactile.[4,5] For example, odor sensitivity is impaired in children with ADHD and stimulant medications improve this problem.[6] The effects of stimulants are not just limited to olfactory function; they also affect visual[7] and auditory information processing.[8,9]

Tactile sensory processing problems are also involved in ADHD.[5,10] There are different types of sensory problems in children with ADHD, including tactile defensiveness, hyposensitivity to touch, and poor tactile perception.[4] Self biting or punching and the desire to touch rough surfaces are two kinds of hyposensitivity to touch that children with ADHD may experience. Hyposensitivity to touch is in a negative association with anxiety.[4] On the other hand, methylphenidate (MPH) increases pain threshold by altering noradrenergic and serotoninergic transmission in the spinal cord;[11] it also has antinociceptive effects.[12] Nail biting is a common behavioral problem in the clinical sample of children with ADHD.[13]

Sensory processing has been suggested as a guide for pharmacological treatment in autistic disorders.[14] A study reported that good response to MPH (Ritalin®, Novartis Pharmaceuticals Corp., East Hanover, New Jersey) in children with ADHD can be predicted before starting the medication by sensory integrative testing.15 In this article, the author reports an association between methylphenidate and sensory processing problems in two children with ADHD.

Case Reports

Case 1. A six-year-old boy was referred to the author’s clinic with hyperactivity, impulsivity, and inattentiveness. He was diagnosed with ADHD using the Diagnostic and Statistical Manual for Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR) diagnostic criteria.[16] He had been taking MPH 10mg twice daily for two years. Six months ago, his family and teacher began complaining about his disruptive behaviors. The medication was titrated to 30mg/day (20mg in the morning and 10mg in the afternoon). After increasing his dosage, he began frequently biting his nails to the point of nail damage and bleeding. The dosage was then decreased to 10mg two times per day. The nail biting stopped. Two weeks later, MPH was increased to 30mg/day. The nail biting started soon afterward. The trial of increasing and then decreasing the dosage of MPH was conducted three times. The nail biting reappeared after increasing MPH every time. According to his mother’s report, nail biting occurred about one hour after taking 20mg of MPH (in the morning). The nail biting would last about two hours and gradually cease. He did not bite his nails after taking the 10mg dose of MPH. There was a positive history of nail biting three years previously, before taking MPH, that spontaneously resolved. He did not experience nail biting during the two years he was taking 10mg of MPH two times per day.

There were no comorbid psychiatric disorders, such as separation anxiety disorder, obsessive compulsive disorder, posttraumatic disorder, and major depression. No laboratory examination finding or marked medical condition, such as thyroid function impairment, was found. His mother reported that his ability to detect, identify, and discriminate smells was very high and stronger than other children his age. He would usually react negatively to or express dislike for smells that would not seem to bother or be noticed by other children. In addition, he was easily distracted by sounds not usually noticed by others (e.g., humming of refrigerators, fans, or heaters or the ticking of clocks). He also liked to touch many things, including other people.

Case 2. An eight-year-old girl was referred to the author’s clinic for inattentiveness and hyperactivity. The patient and her parents were interviewed. Her teacher’s report was taken. ADHD diagnosis was made according to DSM-IV-TR diagnostic criteria and Kiddie Schedule for Affective Disorders and Schizophrenia (K-SADS)-Farsi Version.[17] She had clinically estimated mild mental retardation. Five milligrams per day of MPH was administered and increased to 5mg two times per day after one week. She started lip biting about half an hour after taking the first dosage of the medication. The lip biting continued for about four hours. This pattern repeated after each session of taking the mediation. Her parents indicated a severity of lip biting on a 10-cm-long line with anchors of ‘no lip biting’ and ‘the worst possible lip biting with change of color of the lip or bleeding of lip’ (a visual analog scale). The severity of lip biting was 1 to 2 before taking medication or after discontinuation of it. It increased to 7 to 9 after taking medication. The medication was discontinued. The lip biting disappeared immediately. A few days later, MPH was readministered and the lip biting immediately reemerged after the first dose of the medication. MPH administration was rechallenged three times. No laboratory examination finding or marked medical condition, such as thyroid function impairment, was found. The patient and her family did not have a remarkable history for psychiatric disorders and general medical problems.


The patient in Case 1 experienced nail biting after taking a single dose of MPH (20mg) in the morning while he did not experience  nail biting after taking the 10mg dosage of MPH in the afternoon. He did not experience nail biting after decreasing the dosage. The different trials of MPH in Case 1 suggested to the author that the patient’s nail biting was related to the higher dosages of MPH.

Hypersensitive or inappropriate responses to smell are also a type of sensory processing problem. In Case 1, the smell and auditory sensory systems did not appear to be functioning properly because the patient experienced distress from smell and noise sensations that were not noticed by other people. This suggested to the author that there was a sensory processing problem. Children with touch hyposensitivity may crave touching everything and everyone. The stereotypic behavior of nail biting might be a type of tactile hyposensitivity.[4]

Tactile information or experiences are relayed to the brain from the skin. Under-responsiveness or low registration to tactile information is a type of reaction impairment to sensory input. In other words, a low level of input might not lead to a response and a high level of input is necessary to have a response, suggesting an overmodulating response.[18] These children may also be self-abusive by pinching and biting themselves.

With consideration that sensory modulation disorder has been reported in many children with ADHD,[2] one of the goals of treatment of children with ADHD could be addressing sensory processing problems. In other words, normalization of the sensory integration by improving the way the nervous system registers and interprets sensory information should be one of the goals.

The cases in this report suggest that MPH may be associated with negative behaviors, such as nail biting and lip biting, or exacerbate tactile hyposensitivity. Awareness of sensory processing problems in children with ADHD, such as tactile hyposensitivity and hypersensitivity to sounds and smells, might guide us in the pharmacological management of these children.

Another possible explanation is that the children are suffering from ADHD and some symptoms that are usually detected in pervasive developmental disorder. Further studies should investigate whether there is a disorder with an overlap of both of ADHD and pervasive developmental disorders symptoms. This supports the finding that ADHD is not an exclusive diagnosis in children with pervasive developmental disorder.[19] In addition, a recently published study20 reported that there is a phenotypical overlap between ADHD and autistic disorders. The authors of that study suggested that there are two subtypes of ADHD co-occuring with autism, including inattentive-stereotyped and hyperactive-communication impaired.[20] These two different subtypes are in association with two different neurochemical dopaminergic and serotenergic pathways. Further studies should survey if MPH can exacerbate some stereotypical behavior, such as nail biting, in children with ADHD and sensory processing problems. Further studies could be conducted using somatorsensory-evoked potential, power spectrum, and quantitative electroencephalogram (EEG) to understand more about the sensory problems and their association with medication.

Limitations of this report are that it is only two cases of a limited adverse event and cannot be generalized to all children with ADHD. It should be emphasized that there may be a possible association between MPH and exacerbation of sensory processing problems, not a cause and effect relationship. Controlled studies are required to research these possible effects. These possible associations will be controversial until more evidence of a cause-and-effect relationship is found.

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