Nondermatomal Somatosensory Deficits
Nondermatomal somatosensory deficits (NDSDs) are sensory deficits that don't conform to the distribution of peripheral nerves or dermatomes, typically seen in the setting of chronic pain and following physical trauma.
Epidemiology and Risk Factors
NDSDs are seen in 25-50% of patients with chronic pain.
A study compared two groups of inpatients with chronic pain, 90 of which had NDSDs and 90 did not. A history of physical trauma was associated with the NDSD group. Personality disorder and adverse childhood experiences was associated with the non-NDSD group. There was no difference in the rates of depression and anxiety.
The aetiology is usually considered to be functional with a multifactorial aetiology.
There are certain organic causes for hemisensory syndrome in association with chronic pain such as thalamic stroke. Conditions such as carpal tunnel syndrome commonly present with symptoms and signs that don't conform to known variants of the distribution of the median nerve.
Sensory Deficits: The onset of the sensory deficit is typically gradual but abrupt presentations can occur. The primary deficits are reduced pinprick sensation, insensitivity to deep tissue pressure, or both. 
The distribution may be quadratomal (i.e. one limb) or hemibody on the same side as the chronic pain. In nonorganic causes of hemisensory syndrome there is often an exact splitting at the midline. Certain areas may retain normal sensation within the affected quadratomal or hemibody zone such as the head, nipple, or genitals. The border of the sensory deficit may vary depending on the direction and pattern of the applied stimuli.
Chronic Widespread Pain: The sensory deficits change in association with changes in pain. The pain is often burning or deep aching in quality. The patient is usually more concerned about the pain than the sensory deficit.
Motor Function: There is often an accompanying parallel and unusual alteration in motor function. However anaesthetic hands often retain the ability for complex delicate movements.
The clinician should have some caution in applying the term "nondermatomal," firstly because of the myriad of anatomical variations, and secondly because such sensory deficits may resolve upon effective treatment of the primary pain condition.
- Mailis-Gagnon A, Nicholson K. On the nature of nondermatomal somatosensory deficits. Clin J Pain. 2011 Jan;27(1):76-84. doi: 10.1097/AJP.0b013e3181e8d9cc. PMID: 20664332.
- Egloff N, Maecker F, Stauber S, Sabbioni ME, Tunklova L, von Känel R. Nondermatomal somatosensory deficits in chronic pain patients: are they really hysterical? Pain. 2012 Sep;153(9):1847-1851. doi: 10.1016/j.pain.2012.05.006. PMID: 22867972.
- Vicotr Rues. Functional Neurologic Symptom Disorders. Aminoff’s Neurology and General Medicine, Fifth Edition. Elsevier 2014