Ixekizumab was approved by the US Food and Drug Administration for plaque psoriasis after 3 clinical trials—UNCOVER-1, UNCOVER-2, and UNCOVER-3—were performed. In UNCOVER-3, the most common side effects that occurred—nasopharyngitis, upper respiratory tract infection, injection-site reaction, arthralgia, headache, and infections (specifically candidiasis)—generally were well tolerated. More serious adverse events included cardiovascular and cerebrovascular events, inflammatory bowel disease, and nonmelanoma skin cancer.3
Notable laboratory abnormalities that have been documented from ixekizumab include elevated liver function tests (eg, alanine aminotransferase, aspartate aminotransferase, bilirubin, and alkaline phosphatase), as well as leukopenia, neutropenia, and thrombocytopenia.4 Although short-term thrombocytopenia, as described in our patient, provides an explanation for the bruising noted on observation, it is unusual to note such notable ecchymoses within days of the first injection.
Onycholysis has not been documented as a side effect of ixekizumab; however, it has been reported as an adverse event from other biologic medications. Sfikakis et al5 reported 5 patients who developed psoriatic skin lesions after treatment with 3 different anti-TNF biologics—infliximab, adalimumab, or etanercept—for rheumatoid arthritis; 2 of those patients also developed nail changes consistent with psoriatic onycholysis. In all 5 patients, symptoms of rheumatoid arthritis improved despite the new-onset skin and nail psoriasis.5
The exact pathophysiology of these adverse events has not been clearly understood, but it has been proposed that anti-TNF biologics may initiate an autoimmune reaction in the skin and nails, leading to paradoxical psoriasis and nail changes such as onycholysis. Tumor necrosis factor may have a regulatory role in the skin that prevents autoreactive T cells, such as cutaneous lymphocyte antigen–expressing T cells that promote the formation of psoriasiform lesions. By inhibiting TNF, there can be an underlying activation of autoreactive T cells that leads to tissue destruction in the skin and nails.6 Anti-TNF biologics also could increase CXCR3, a chemokine receptor that allows autoreactive T cells to enter the skin and cause pathology.7
IL-17A and IL-17F also have been shown to upregulate the expression of TNF receptor II in synoviocytes,8 which demonstrates that IL-17 works in synergy with TNF-α to promote an inflammatory reaction.9 Due to the inhibitory effects of ixekizumab, psoriatic arthritis should theoretically improve. However, if there is an alteration in the inflammatory sequence, then the regulatory role of TNF could be suppressed and psoriatic arthritis could become exacerbated. Additionally, its associated symptoms, such as dactylitis, could develop, as seen in our patient.4 Because psoriatic arthritis is closely associated with nail changes of psoriasis, it is conceivable that acute arthritic flares and acute onycholysis are both induced by the same cytokine dysregulation. Further studies and a larger patient population need to be evaluated to determine the exact cause of the acute exacerbation of psoriatic arthritis with concomitant nail changes as noted in our patient.
Acute onycholysis (within 72 hours) is a rare side effect of ixekizumab. It can be postulated that our patient’s severe acute onycholysis associated with a flare of psoriatic arthritis could be due to idiosyncratic immune dysregulation, promoting the activity of autoreactive T cells. The pharmacologic effects of ixekizumab occur through the inhibition of IL-17. We propose that by inhibiting IL-17 with associated TNF alterations, an altered inflammatory cascade could promote an autoimmune reaction leading to the described pathology.