Analgesia or hypoalgesia refers to a complete loss or diminution, respectively, of pain sensation, or the absence of a pain response to a normally painful stimulus. These negative sensory phenomena may occur as one component of total sensory loss (anesthesia) or in isolation. Consequences of analgesia include the development of neuropathic ulcers, burns, Charcot joints, even painless mutilation or amputation.
Analgesia may occur in:
- peripheral nerve lesions, e.g., hereditary sensory and autonomic neuropathies (HSAN), leprosy;
- central spinal cord lesions which pick off the decussating fibers of the spinothalamic pathway in the ventral funiculus (with corresponding thermoanesthesia), e.g., syringomyelia;
- cortical lesions, e.g., medial frontal lobe syndrome (akinetic type).
Congenital syndromes of insensitivity to pain were once regarded as a central pain asymbolia (e.g., Osuntokun’s syndrome), but on further follow-up some have turned out to be variants of HSAN.
Larner AJ, Moss J, Rossi ML, Anderson M. Congenital insensitivity to pain: a 20 year follow up. Journal of Neurology, Neurosurgery and Psychiatry 1994; 57: 973-974