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:
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 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.