Specific terms are used to describe the increase in pain observed in the presence of injury or disease. An increase in pain in response to normally painful stimuli is referred to as hyperalgesia (27). In contrast, the perception of pain in response to stimuli that are normally not perceived as painful is referred to as allodynia (1,27). One of the most common positive signs (28) associated with peripheral neuropathy is pain in response to light brushing of skin, a normally innocuous stimulus (29). Pain in response to such innocuous stimuli is referred to as dynamic mechanical allodynia. Hyperalgesia may reflect an increase in the excitability of tissue nociceptors, as well as neurons in the CNS involved in nociceptive processing. This increase in excitability is referred to as sensitization. In contrast, dynamic mechanical allodynia appears to be conveyed by low-threshold afferents impinging on a sensitized CNS (30). The vast majority of dorsal horn neurons receiving input from visceral structures also receive input from somatic structures (so-called convergent input), in particular, those overlying the visceral organ in question. Consequently, injury or inflammation of a visceral structure may result in hyperalgesia or allodynia in the somatic structure overlying the inflamed visceral organ. Such hyperalgesia and allodynia is called referred hyperalgesia and referred allodynia, and again reflects sensitization of neurons within the CNS (31).
Was this article helpful?
This guide will help millions of people understand this condition so that they can take control of their lives and make informed decisions. The ebook covers information on a vast number of different types of neuropathy. In addition, it will be a useful resource for their families, caregivers, and health care providers.