Psoriasis, Psoriatic Arthritis Linked to Factors Contributing to Polyneuropathy Risk

Pietro E. Doneddu, MD

Credit: Humanitas University

A new study suggests psoriasis and psoriatic arthritis (PsA) are linked to an increased risk of developing contributing factors for polyneuropathy rather than a direct neuropathy risk.¹

“If confirmed by additional studies, polyneuropathy should be included among the potential comorbidities associated with psoriasis and psoriatic arthritis,” wrote investigators led by Pietro E. Doneddu, MD, from the Neuromuscular and Neuroimmunology Unit at IRCCS Humanitas Research Hospital in Italy.

Psoriasis is often associated with PsA and comorbidities such as cardiovascular disease, metabolic syndrome, obesity, hypertension, dyslipidemia, diabetes mellitus, anxiety and depression, inflammatory bowel disease, cancer, kidney disease, sleep apnea, chronic obstructive pulmonary, uveitis, and hepatic disease.² A previous study from the late 80s saw a link between neurologically medicated inflammation and psoriasis.³

More than 30 years later, the peripheral neuropathy risk in psoriasis or PsA was unknown. Thus, investigators sought to assess the neuropathy risk among patients with psoriasis or PsA.¹

Investigators conducted a study with 100 patients with psoriasis (n = 31) and PsA (n = 69) enrolled at rheumatological and dermatological outpatient clinics at Humanitas Research Hospital in Milan, Italy, from January 2020 – December 2022, and 100 controls. Patients with psoriasis and PsA had a median disease duration of 15 years. Polyneuropathy was diagnosed through an electrophysiological examination, skin biopsy, and nerve ultrasound.

In total, 9 patients were diagnosed with polyneuropathy, and no controls had this condition (relative risk [RR], 19.00; 95% confidence interval [CI], 1.12 – 322.11). Patients with psoriasis and PsA had a polyneuropathy relative risk of 22.09 (95% CI, 1.17 – 416.43) and 18.75 (95% CI, 1.07 – 327.62, respectively).

All patients with a clinical diagnosis of peripheral neuropathy underwent electrophysiological examination (nerve conduction study and needle electromyography). During this, investigators evaluated the following nerves on the right side: median, ulnar, tibial, peroneal, sural, superficial peroneal, radial sensory, vagus, and roots C5 and C6.

Additionally, laboratory tests evaluated glucose, glycated hemoglobin, complete blood test, creatinine, vitamins, copper, liver function tests, alanine aminotransferase, serum and urine immunofixation test, urine kappa and lambda light chains, thyroid stimulating hormone, C-reactive protein, anti-nuclear antibodies, extractable nuclear antigen, anti-neutrophil cytoplasmic antibodies, HBsAg, HBsAb, HBcAg, HBcAb, antibodies to hepatitis C virus, and human immunodeficiency virus. Patients with symptoms and signs of small fiber neuropathy and normal nerve conduction studies had skin biopsies, and patients with Lyme disease were tested for Borrelia burgdor-feri antibodies.

Moreover, each participant was asked if they had any comorbidity, especially those linked to an increased risk of peripheral neuropathy. Compared to the control group, patients with psoriasis or PsA had a greater prevalence of the following comorbidities: cardiovascular diseases or arterial hypertension of dyslipidemia (52% vs 35%), autoimmune diseases (22% vs 12%), cancer (9% vs 1%), diabetes mellitus (8% vs 2%), fibromyalgia (8% vs 0%), chronic kidney disease (5% vs 0%), MGUS (3% vs 0%), and HCV and cirrhosis (2% vs 0%).

The team observed polyneuropathy was length-dependent, symmetrical, and predominantly sensory. These patients had minimal or no disability. Furthermore, comorbidities and exposure to therapies known to increase the polyneuropathy risk were more frequent in patients with psoriasis or PsA (42%) compared to controls (4%) (P = .0001).

“Although nerve US was only performed on a limited number of patients, our study suggests that focal nerve enlargement outside of entrapment sites is a common finding and relatively widespread, particularly in the lower limbs, among patients with psoriasis/psoriatic arthritis and polyneuropathy,” investigators wrote. “It is important to note that the presence of nerve enlargement is not specific to a single disease and has been observed in conditions such as chronic inflammatory demyelinating polyneuropathy, Guillain–Barré syndrome, multifocal motor neuropathy, hereditary neuropathies, and diabetic neuropathy.”

Despite the observed greater polyneuropathy risk in patients with psoriasis or PsA, an analysis excluding possible contributory causes demonstrated the risk was insignificant.

“Our study also suggests that psoriasis and psoriatic arthritis are not associated with an elevated risk of nerve entrapments,” investigators concluded.

References

1. ^{Doneddu PE, Borroni R, Ceribelli A, et al. Risk of peripheral neuropathy in patients with psoriasis and psoriatic arthritis. A prospective cohort study. Muscle Nerve. Published online June 28, 2024. doi:10.1002/mus.28196}
2. ^{Related Conditions of Psoriasis. National Psoriasis Foundation. https://www.psoriasis.org/related-conditions/. Accessed July 8, 2024.}
3. ^{Naukkarinen A, Nickoloff BJ, Farber EM. Quantification of cutaneous sensory nerves and their substance P content in psoriasis. J Invest Dermatol. 1989;92(1):126-129.}