Chronic Inflammatory Demyelinating Polyneuropathy

Chronic Inflammatory Demyelinating Polyneuropathy (CIDP) is an acquired, immune-mediated demyelinating polyneuropathy that affects peripheral nerves and nerve roots. It has an extremely variable presentation and is often difficult to diagnose. It is important to be aware of as an MSK physician because pain can be one of the manifestations.
== Epidemiology ==
The prevalence has been estimated to be between 0.67-10.3 per 100,000 people. There is an increasing incidence and prevalence with age. It is two times more common in men than women. There are no clear predisposing risk factors.
In neuromuscular disease referral centres, CIDP is determined to be the cause of around 20% of all undiagnosed neuropathies, and 10% of all patients referred.Case Files Neurology. 2017
== Pathogenesis ==
The aetiology is immunologic through cell-mediated and antibody-mediated mechanisms. There is persistent multi-focal demyelination that has a predilection for the spinal roots, major plexuses, and proximal nerve trunks. Histologically there are patchy areas of demyelination and oedema with variable inflammatory infiltrates of macrophages and T cells.
== Clinical Features ==
CIDP should be considered in any patient with progressive symmetrical or asymmetrical polyradiculopathy that is relapsing and remitting or that progresses for longer than 2 months.
The pace of onset is usually chronic, but can sometimes be more acute. There is a temporal continuum between the demyelinating form of Guillain-Barre on the one end (acute inflammatory demyelinating polyneuropathy - AIDP), and CIDP in those with AIDP that don't recover. Some patients will follow a relapsing course.
Patients usually complain of a generalised pattern of numbness and weakness in the upper and lower extremities along with spontaneous pain. Some patients may present with a progressive sensory ataxia, while in other motor symptoms are more dominant. 
The common manifestations of CIDP are: 	Prevalence
Gradually worsening paraesthesia and numbness 	72-89%
Muscle weakness in legs and arms 	83-94%
Areflexia without wasting 	86-94%
Facial palsy 	4-15%
Preferential loss of joint position or vibration sense	
Foot drop and difficulty getting out of the chair 	
Difficulty with fine motor control 	
Sensory ataxia 	
Fatigue 	
Severe Pain 	13-17%
Notably motor and proprioceptive deficits predominate over pain and autonomic symptoms. Severe pain occurs in 13-17% of patients.
The typical form of CIDP (>50%) is a sensory-motor phenotype. The symptoms are usually proximal rather than distal and roughly symmetrical. The acute form (18%) manifests with both proximal and distal symptoms. Atypical forms include a predominant distal distribution (distal acquired demyelinating symmetric - DADS), an asymmetric distribution (multifocal acquired demyelinating sensory and motor neuropathy - MADSAM), pure sensory, pure motor, and extremely rarely focal CIDP.
== Investigations ==
The major tests are EMG/NCS, CSF examination, nerve biopsy, MRI, and blood tests.
* CSF shows increased protein content and reduced cell count (called cyto-albuminologic dissociation).
* Neurophysiology results may be non-specific and show mixed results because of the concomitant secondary axon degeneration on top of the demyelination. There is also a high prevalence of user error in the electrophysiology technique and interpretation.
* Nerve biopsy is at risk of sampling error when a biopsy is taken proximal to the site of biopsy showing only nonspecific lesions.
* MRI can provide supportive information such as hypertrophy and high signal in the nerve roots and plexi.
* Skeletal surveys or scintigrophy: Can be done to detect plasmacytoma or myeloma.
* Blood tests: tests are done to rule out other causes or associated conditions: FBC, HbA1c, creatinine, electrolytes, LFTs, TSH, B12/folate, protein electrophoresis, light chains. Additional tests to consider are HIV, neuroborreliosis, and ANA.
== Diagnosis ==
Diagnosis is difficult and misdiagnosis is very common in general neurology practice.
There are at least 15 different diagnostic criteria. See below for an example from the European Federation of Neurological Societies and the Peripheral Nerve Society. The criteria are highly specific (96.2%) but not sensitive (81.3%). Clinical history, physical examination, Electrophysiology studies, and laboratory tests form part of the criteria. Misdiagnosis is common, with misinterpretation of nerve conduction studies being a common reason.
== Differential Diagnosis ==
The list of differentials is extensive.
== Treatment ==
Corticosteroids, intravenous immunoglobulin, plasma exchange, immunosuppresive drugs.
== Resources ==
See Ryan et al for an open access review. 
==References==
Category:Polyneuropathies