By Michael Rubin, MD
Professor of Clinical Neurology, Weill Cornell Medical College
SYNOPSIS: Chronic inflammatory demyelinating polyneuropathy (CIDP) usually is diagnosed in patients who have a generalized disorder. However, there are focal syndromes that have been observed and diagnosed under different names that meet many of the clinical and electrodiagnostic criteria of CIDP and may be referred to as “focal” CIDP.
SOURCE: Benoit C, Svahn J, Debs R, et al. Focal chronic inflammatory demyelinating polyradiculoneuropathy: Onset, course, and distinct features. J Peripher Nerv Syst 2021;26:193-201.
Chronic inflammatory demyelinating polyneuropathy (CIDP) is an acquired, immune-mediated, inflammatory demyelinating neuropathy. CIDP typically manifests as a symmetric, motor-predominant neuropathy with proximal and distal weakness, but may begin focally and remain so (referred to as focal CIDP), affecting either the brachial or lumbosacral plexus, or a nerve or several nerves in a single limb. Autoimmune neuropathies, such as multifocal motor neuropathy with conduction block (MMNCB) or multifocal acquired demyelinating sensory and motor neuropathy (MADSAM or Lewis-Sumner syndrome), are asymmetric variants of CIDP. These types also may have a focal onset, and remain so for years or decades, and may or may not be focal CIDP. Cases of idiopathic chronic brachial or lumbosacral plexopathy, with nerve root thickening on magnetic resonance imaging (MRI) and responding to intravenous immunoglobulin (IVIG), also may represent focal CIDP. Can these entities be teased apart from focal CIDP, or is focal CIDP an autoimmune neuropathy with a focal onset?
Patients with focal CIDP, limited to a single limb for two years or more, were selected from the CIDP database of the Pitie-Salpetriere Hospital, Paris, (2005-2018) and the Pierre Wertheimer Hospital, Lyon, (2010-2017) if they fulfilled European Federation of Neurology Society-Peripheral Nervous System (EFNS-PNS) clinical and electrodiagnostic criteria for CIDP. Absent electrodiagnostic criteria, they were diagnosed with focal CIDP if they fulfilled at least two supportive clinical criteria.
Patients were excluded if they demonstrated clinical characteristics consistent with Parsonage-Turner syndrome, electrodiagnostic findings suggestive of hereditary neuropathy with pressure palsies (HNPP), imaging findings suggestive of neoplastic disease, autoimmune conditions other than CIDP, or findings suggestive of motor neuron disease. Electrodiagnostic studies were performed using standard procedures, and somatosensory evoked potential (SSEP) studies were performed when warranted to evaluate proximal demyelination.
Patients were categorized as focal brachial or lumbosacral inflammatory demyelinating plexus neuropathy (F-PN), focal demyelinating sensory and motor neuropathy (F-SMN), or focal demyelinating motor neuropathy (F-MN). The latter two categories required involvement of a single nerve or multiple peripheral nerves, respectively. IVIG or oral steroids were used for treatment, with response defined as improvement of two or more Medical Research Council (MRC) grades. Statistical analysis comprised the chi-square and Kruskal-Wallis tests, with P < 0.05 defined as significant.
Among 30 focal CIDP patients, 18 had F-PN, seven had F-SMN, and five had F-MN. F-PN patients had motor nerve conduction abnormalities in 39%, but 80% demonstrated proximal demyelination based on SSEP study. All had focal hypertrophy or increased short tau-inversion recovery image signal intensity on plexus MRI. Abnormalities remained monomelic in 94% of F-PN patients but spread to other limbs in 57% and 40% of F-SMN and F-MN patients, respectively. Overall, Neuropathy Limitations Scale (ONLS) was best for F-PN, with none having a score > 2 at the final visit, compared to 43% and 40% for F-SMN and F-MN, respectively. Focal CIDP appears to encompass at least three entities, and F-SMN and F-MN are more likely to progress to a multi-limb MADSAM or MMNCB phenotype.
COMMENTARY
Atypical forms of CIDP vary, not only in phenotype but also in response to immunotherapy. Distal acquired demyelinating symmetric polyneuropathy (DADS), characterized by symmetric, demyelinating, sensory, length-dependent polyneuropathy, typically is more responsive to rituximab than IVIG, whereas MADSAM, a chronic, progressive, demyelinating mononeuropathy multiplex, responds to IVIG, but less favorably than does CIDP. IVIG is the treatment of choice for pure motor CIDP, as well as for focal CIDP and pure sensory CIDP, although the latter often requires maintenance therapy.1
REFERENCE
- Menon D, Katzberg HD, Bril V. Treatment approaches for atypical CIDP. Front Neurol 2021;12:653734.
