These are group of painful conditions in which the nociceptive impulses are carried in an exaggerated way, with symptoms of lancinating /shooting pain to an innocuous like slight touch. In majority of cases it is followed by some form of trauma. The intensity of trauma and type of injury has no relations with the development CRPS. The symptoms will not respond to any of the conventional analgesics.
The taxonomy of CRPS was introduced in 1993 by the International Association for the Study of Pain (IASP) to describe the pain syndrome more accurately. The term Regional refers to the fact that the pain is located in one region of the body however, the condition can spread to additional areas. It is divided into:
- Type-I or reflex sympathetic dystrophy in which injury occurs to the skin, bones, joints or tissue.
- Type-II or causalgia in which injury occurs to major nerves.
Autonomic Nervous System (ANS) is divided into sympathetic & parasympathetic systems. Sympathetic system is involved in CRPS. The neurons of Autonomic Nervous System (ANS) are classified into pre-ganglionic and postganglionic neurons depending on the connection with ganglia. The pre-ganglionic fibers arise from Central Nervous System (CNS) and carry impulses to the ganglion. While the postganglionic fibers arise from ganglion and supply signals to smooth muscles and glands. The neurotransmitter at the terminals of pre-ganglionic sympathetic and parasympathetic system is acetylcholine. Acetylcholine is also liberated at postganglionic parasympathetic terminals. The neurotransmitter at the terminals of postganglionic sympathetic system are adrenaline and nor-adrenaline except for sweat glands (postganglionic sympathetic system) where acetylcholine is liberated.
The pathophysiology of CRPS is poorly understood. The theory of development of CRPS is based on dysfunction of the sympathetic nervous system. A peripheral inflammatory component is also thought to play a role. The condition is usually initiated by trauma, often involving the hands or feet. CRPS has also been reported as an complication of minor surgical procedures. In addition, the syndrome has been reported following nerve injury caused by intramuscular injection or routine venipuncture and as an adverse reaction to subcutaneous allergic reaction. CRPS has also been associated with medical conditions such as diabetic neuropathy, multiple sclerosis, myocardial infarction and cancerous infiltration of a nerve plexus.
The afferent fibers might be sensitized by chemicals released from sympathetic terminals resulting in aberrant activity for any stimulus. There can be abnormal coupling between afferent somatic sensory nerves and efferent sympathetic fibers leading to aberrant impulses. This abnormal physiological situation sensitizes the central nervous system leading to exaggerated pain signals for harmless stimulation.
CRPS comprises of following signs & symptoms. They are:
- Pain: characterized as aching, burning, pricking or shooting.
- Sensory changes: allodynia (pain on touch), hyperalgesia (exaggerated pain on pin prick.
- Autonomic dysfunction: abnormalities of skin temperature,
- Movement disorders: painful movement of joints
- Psudomotor changes: change of in skin color & texture.
- Dystrophy and atrophy: fall of hail follicles, atrophy of skin, muscles or bone.
Pain, oedema and autonomic dysfunction predominate early in the course of CRPS, whereas the movement disorders, dystrophy and atrophy are more important in the later stages of illness. In its early stages it is usually sympathetically maintained but with time it becomes sympathetically independent. It spreads in specific patterns and may become generalized to involve the entire limb or body.
Stages of CRPS
Patient complains of severe pain usually of a burning quality associated with cyanosis & mottling. Swelling is disproportionate to the injury. The pain does not follow any dermatomal distribution pattern, and hence it is termed as regional. The majorities of patients suffer some degree of autonomic dysfunction manifesting as hypothermia or hyperthermia, hyperhidrosis and sympathetically induced changes in hair and nail growth.
All of the components of the stage I process are noted, but dystrophy of the integument is more pronounced. The pain spreads both regionally and proximally, oedema is more evident and motor manifestations become more intense. In late stage II disease patients usually have a cold, dusky, cyanotic extremity with marked brawny oedema.
The pain spreads further up the proximal extremity and may spread in a mirror fashion to the contralateral extremity or ipsilaterally down the trunk and leg to involve the entire body surface. Atrophic features are obvious, and the integument and soft tissues begin to atrophy. At this stage, in areas where hair growth was increased, patients lose hair, the skin further thickens and the nails continue to grow too rapidly.
- Alpha blockers like prazosin, phenoxybenzamine can provide sympathetic denervation at nerve terminals.
- Tricyclic antidepressants: The drugs commonly used are amitriptyline, nortriptyline.
- Anticonvulsants like gabapentin may give some relief.
- Clonidine: It works by stimulating inhibitory descending inhibitory pain pathways that are norepinephrine dependent.
- Calcium channel blockers like verapamil, nifedepine may be used.
- NMDA receptor antagonists like ketamine and methadone may be tried.
- Baclofen having role on descending inhibitory pathway may be tried.
- Opioids like tramadol or combinations with paracetamol may be tried to control pain.
Interventional Pain Management:
1. SYMPATHETIC BLOCKADE: Neurolytic sympathetic block gives excellent result in many cases if performed early. Diagnostic sympathetic nerve blocks involve injecting local anaesthetic drugs around sympathetic chain of the region and should be done prior to neurolytic block. The local anaesthetic blocks provide immediate relief but they are not long lasting. Long lasting or permanent relief may be obtained with repeated block with depo-steroids (5-7 times), blocking with neurolytic agents or blocking with radio-frequency generator. Neurolysis with radio frequency gives best results. Commonly performed sympathetic blocks depending on the body parts involved are: Stellate ganglion block, Lumbar sympathetic blockade, Superior Hypogastric block, Thoracic sympathetic block, Ganglion Impar block etc.
2. INTRAVENOUS REGIONAL SYMPATHETIC BLOCKADE: This procedure is similar to Bier’s block with the drugs like guanethedine, bretylium etc. But not done nowadays.
3. SIPINAL CORD STIMULATION: It has very important role in treating CRPS, especially in refractory cases.
4. INTRATHECAL DRUG DELIVERY SYSTEM: Intrathecal drug delivery can be employed to treat CRPS patients who have a significant component of dystonia, failed neurostimulation, long standing disease, multilimb involvement, or need palliative care.