Neuropathies in Rheumatic Diseases Encompass Wide Spectrum of Diagnoses

VBCR - October 2016, Vol 5, No 5 - Rheumatic Diseases
Wayne Kuznar

Up to 40% of patients with rheumatic diseases will have neuropathies attributable to competing disorders. These competing comorbidities may encapsulate many different syndromes. Using the VITAMINS mnemonic may help to distinguish between neuropathies caused by rheumatic diseases versus those caused by competing morbidities, said Julius Birnbaum, MD, Assistant Professor of Medicine and Neurology, The Johns Hopkins Hospital, Baltimore, MD, at the 9th Annual Rheumatology Nurses Society Conference.

“If you use this VITAMINS mnemonic at the bedside, you’ll be able to go through and make sure that you are able to recognize neuropathies that are not necessarily due to an autoimmune disorder,” said Dr Birnbaum. The mnemonic is as follows:

V
Vascular diagnoses (ie, systemic vasculitides and vasculitis resulting from an infection)
I
“Infections are a big cause of neuropathies in patients we care for, particularly HIV [human immunodeficiency virus], hepatitis B, hep­atitis C, even mycobacterial and fungal diseases, because depending on the rheumatic disease, these patients tend to be prominently immunosuppressed,” he said
T
Traumatic (eg, carpal tunnel syndrome)
A
Autoimmune/inflammatory disorders, with the 2 main culprits being celiac disease and sarcoidosis
M
Metabolic disorders, mostly diabetes, but “what’s underappreciated is that an impaired glucose tolerance test may cause neuropathies that are every bit as painful as someone with diabetes,” Dr Birnbaum explained. “This is really important due to the use of corticosteroids in our patients.” He recommended obtaining a fasting 2-hour glucose tolerance test
I
Inflammatory disorders, such as paraproteinemia, and cryoglobulinemia, are less common causes of neuropathy in patients with rheumatic disease
N
Neoplastic disorders, especially paraneoplastic syndromes, which represent an immune-mediated response against a cancer. “The response is dysregulated, and the peripheral nerves are affected as a byproduct,” said Dr Birnbaum
S
Structural “mimics” (eg, syringomyelia and myeloradiculopathy).

Classifying Peripheral Neuropathies

Demyelinating neuropathies (eg, compressive neuropathies, Guillain-Barré syndrome, and chronic inflammatory demyelinating polyneuropathy) are neuropathies in which the axon has not been severed but the myelin sheath surrounding the axon has been stripped away. In this case, impaired conduction may cause neuropathy. These demyelinating neuropathies occur infrequently in patients with rheumatic diseases. “When you have a patient with demyelinating neuropathy and rheumatic disease, such as Guillain-Barré and lupus, we say that these are 2 coincidental unrelated autoimmune disorders,” Dr Birnbaum noted.

Also included in the spectrum of peripheral nervous system manifestations are axonal neuropathies (ie, sensory/sensorimotor polyneuropathies and vasculitic neuropathies). The frequency of symmetric axonal polyneuropathies is approximately 1% to 10% in the context of a rheumatic disease, with vasculitic neuropathies being much less common, he said.

Small-Fiber Neuropathies

Small-fiber neuropathies are an underrecognized entity in the spectrum of peripheral nervous system manifestations, but are “probably the most painful neuropathies that we see,” said Dr Birnbaum. These are painful sensory neuropathies that selectively or predominantly affect unmyelinated nociceptive fibers.

Small-fiber neuropathies cannot be detected by electrodiagnostic studies, which can only test the integrity of larger-fiber myelinated nerves. The small-fiber nerves are electrophysiologically occult, he continued. “If you have a patient with a provocative presentation for a small-fiber neuropathy, so-called ‘normal’ conduction studies may actually support rather than refute your hypothesis that there’s an underlying small-fiber neuropathy,” he said.

A skin biopsy is emerging as the gold standard for small-fiber neuropathy.

Small-fiber neuropathies associated with Sjögren’s syndrome have a distinctive immunologic pattern according to the type of neuropathy, said Dr Birnbaum. Nonataxic sensory neuropathy is characterized by a lower frequency of B-cell activation markers, whereas sensorimotor neuropathy is marked by a high prevalence of B-cell proliferation markers.

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