Two new interventional clinical trials are now recruiting patients with pure MLN, “so there is some hope on the horizon for new therapies for patients with refractory nephrotic syndrome and proteinuria,” said Dr. Ginzler.
Small-Fiber Neuropathies
When his 44-year-old patient with systemic lupus erythematosus (SLE) used highly poetic language to describe widespread pain, her colorful metaphors pointed to a small-fiber neuropathy (SFN) diagnosis, said Julius Birnbaum, MD, MHS, assistant professor of medicine at the Johns Hopkins University School of Medicine in Baltimore.
“She described a sensation of caterpillars with sharp claws crawling up her arms and marching up her neck, hot vats of oil being poured over her thighs, and that her arms and legs ached when she put on any clothes,” he said.
SFNs are sensory, uniformly painful neuropathies that target predominantly unmyelinated C-fiber nerves. Clinical features include burning and lancinating pain, paroxysmal pain and/or intense allodynic pain, he said. SFNs may affect patients with SLE, Sjögren’s syndrome, rheumatoid arthritis, viral and fungal infections, celiac disease, sarcoidosis, scleroderma or diabetes, and it has also been associated with TNF-inhibitor therapy in some patients.5
Look for small fiber deficits on examination: a decrease in pain to pinprick or temperature, and sometimes an increased pain to pinprick hyperalgesia, he said. Nerve conduction studies will be normal, because these only assess the integrity of large-fiber nerves.
Punch skin biopsy on either the proximal thigh or distal leg is the most effective diagnostic tool.6 Look for decreased unmyelinated nerves in the epidermal layer, or “decreased inter-epidermal nerve fiber density” on the pathology report, he said.7 “Punch skin biopsy is easy to do, takes only 15–20 minutes and is minimally invasive. Sensitivity, depending on the underlying neuropathic syndrome, is 60–90% with a specificity above 95%.” Skin biopsy also helps distinguish between length-dependent and non-length-dependent forms of SFN.
‘Whatever treatments are on the horizon, don’t be afraid to tell patients that they have a powerfully painful disorder that will get better, but slowly.’ —Julius Birnbaum, MD, MHS
Patients’ hands may be affected more than their feet, and some have whole-body burning pain, said Dr. Birnbaum. Skin biopsy helps distinguish which neural targets, such as the dorsal root ganglia or the axon, are the sites where pain developed. Quantitative sensory testing (QST) is another method to diagnose SFN, although a patient’s descriptions of the pain are often the best guide.
SFN treatment is challenging, and may require several agents or a combination, said Dr. Birnbaum. Gabapentin, nortriptyline, venlafaxine XR and opioids may be useful, as well as topical agents, such as capsaicin or lidocaine.
