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CSME|CAPDA Medico-Legal Summit - Dr. Angela Mailis
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Unexplainable Sensory Deficits and Intractable Chronic Pain

The term Non Dermatomal Somatosensory Deficits (NDSDs) was coined by Mailis et al (2001) to describe large sensory deficits not conforming to dermatomal/root territories. NDSDs are one of Waddell’s “non organic” signs in chronic pain patients. NDSDS may affect 25-40% of chronic pain patients based on published literature. NDSD borders are non anatomical, sharp or blurred, and can affect the hemibody, a quarter of the body, a limb, or a body area such as face or chest (always at the site of worse pain). NDSDs can be very mild (with slight hypoalgesia/ hypoesthesia to pin prick and touch) or very dense (to the point of complete anesthesia with loss of cutaneous sensation to pin prick, light touch and cold, as well as deep sensory modalities such as vibration, proprioception etc), and are often associated with motor problems (tremors, dystonia, weakness etc.) NDSDs can also be superimposed on structural deficits (eg nerve injury, musculoskeletal conditions etc.) They can be highly variable or extremely fixed over time associated with pain behaviours and significant pain related disability. They mostly occur in the context of emotionally charged conditions (like exposure to a psychotraumatic event); life long stressors; and/or personality organizations (eg. tendency to “convert emotional stressors to physical symptoms”). They may appear after trauma, and evolve/ expand most often as pain worsens or spread, usually within weeks-months post pain onset. The original physical trauma could be insignificant but serve as a trigger of underlying central mechanisms. Rarely, NDSDs occur abruptly at time of the psycho-traumatic event. They have notable associations with female gender, ethnocultural factors, and litigation. Their appearance is a bad prognostic sign for response to treatment or return to work. Of note, most (but not all) patients fulfill criteria for Conversion Disorder. NDSDs respond positively, at least partially, to Sodium Amobarbital (commonly referred to as “Truth Serum”).

NDSDs have similarities with structural deficits (stroke, brachial plexus avulsion etc.) Our group has hypothesized that NDSDs are an unsuccessful attempt of CNS to “shut down pain” by shutting down all peripheral inputs, while pain not only remains but becomes intractable, primarily with burning and aching qualities. Functional imaging by our group (Mailis Gagnon et al, Neurology 2003) indeed demonstrated that NDSD patients have alterations in brain activation patterns. Further research by other teams has further provided evidence suggesting strongly that NDSDs constitute dynamic CNS aberrations as a result of maladaptive neuroplasticity. The interested reader can review this topic in a recent publication (Mailis Angela and Nicholson Keith. NonDermatomal Somatosensory Deficits (NDSDs) and Pain: State of the Art Review, Psychological Injury and Law, Published on line November 3, 2017,

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