Analgesia

Contents

  1. Definition and Clinical Features
  2. Clinical Consequences
  3. Causes and Anatomical Correlates
  4. Congenital Insensitivity to Pain
  5. References

Definition and Clinical Features

Analgesia, or hypoalgesia, refers to a complete loss or diminution, respectively, of pain sensation. It represents the absence of a pain response to a normally painful stimulus. These negative sensory phenomena may occur as one component of a total sensory loss (anesthesia) involving multiple modalities, or they may manifest in isolation.

Clinical testing of pain sensation using pinprick

Analgesia is the loss of pain sensation, often evaluated clinically by assessing the patient's response to a sharp stimulus, such as a sterile pinprick.

Clinical Consequences

Because pain serves a critical protective function, the consequences of analgesia can be severe. Without the ability to feel pain, patients are at a high risk for developing neuropathic ulcers, severe burns, and neuropathic arthropathy (Charcot joints). In extreme cases, it can lead to painless mutilation or unnoticed injuries requiring amputation.

Causes and Anatomical Correlates

Analgesia may occur due to lesions at various levels of the nervous system:

  1. Peripheral Nerve Lesions: Conditions such as hereditary sensory and autonomic neuropathies (HSAN) and leprosy can damage peripheral nociceptive nerve fibers.
  2. Spinal Cord Lesions: Central spinal cord lesions that interrupt the decussating fibers of the spinothalamic pathway in the ventral funiculus can cause analgesia. This is characteristically seen in syringomyelia and is often accompanied by corresponding thermoanesthesia (loss of temperature sensation).
  3. Cortical Lesions: Lesions in the cerebral cortex, such as the medial frontal lobe syndrome (akinetic type), can lead to an altered perception or processing of painful stimuli.

Congenital Insensitivity to Pain

Congenital syndromes of insensitivity to pain were once regarded as a central pain asymbolia (e.g., Osuntokun’s syndrome), where the patient perceives the stimulus but lacks the appropriate emotional or withdrawal response. However, on further follow-up and genetic analysis, some of these cases have turned out to be variants of hereditary sensory and autonomic neuropathies (HSAN).

 

References

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

 

Cross References

Anesthesia; Frontal lobe syndromes