# Understanding the Intricate Pathophysiology of Psoriasis and Related Skin Disorders
## 4 Sporiasis and Associated Dermatologic Disorders
Dermatomyositis (DM) is a rare inflammatory disease that presents distinct cutaneous manifestations and various degrees of potentially life-threatening systemic involvement, such as pulmonary diseases or malignancies [41]. Psoriasis and DM rarely coexist, with only a few cases documented. [PERSON] et al. reported a case of psoriasis combined with DM, and a literature review was performed to speculate on the possible pathogenesis and treatment. In these cases, five were male and ten were female, of which six patients were under 30 years old, and they were all diagnosed with juvenile DM. In six cases, psoriasis occurred before DM, whereas in other cases, DM developed first. Among these cases, one had diabetes, hypertension, and antiglomerular basement membrane disease, another had a hepatic tumor, a third had [PERSON]'s thyroiditis and Sjogren syndrome, and a fourth had interstitial lung disease. Regarding the possible triggers, three cases might be associated with medications, including adalimumab, secukinumab, and withdrawal of prednisolone. One case might have been linked to a hepatic tumor. The patient had no history of medication use or underlying disease. He was a farmer who had been exposed to prolonged sunlight without any protection in the summer. The authors suspected that sunlight exposure could be a possible trigger [47]. Referring to the pathogenesis, sufficient evidence suggested that DM and psoriasis shared some common inflammatory pathways, including IFN-\(\alpha/\beta\)-induced response, INF-\(\gamma\), and TNF-\(\alpha\). In addition, new studies have proved that pDCs are located in the epidermis of DM, which is shared with the pathogenesis of psoriasis. Expression of IL-17 in the cellular infiltrates in both skin lesions may suggest that IL-17 possibly contributes to the development of DM as well as psoriasis [48]. While psoriasis and DM share certain signaling pathways and cytokines, the exact mechanisms behind their co-existence are still not well understood. Based on previous studies, there seems to be a complex, interactive, and self-sustaining inflammatory circuit among these cytokines in psoriasis. As mentioned in the case above, sunlight exposure might play a significant role in the pathogenesis of the co-existence of DM and psoriasis. UV radiation could suppress the IL-23/IL-17 axis, resulting in the inhibition of the production of IL-17. This immune response results in a reduction of IL-17-mediated inflammation in skin lesions, which is similar to the effect of IL-17 inhibitors, and can also disrupt the inflammatory circuit. So, while ultraviolet phototherapy is safe and effective for psoriasis, it is considered a trigger for DM and even exacerbates the symptoms of DM. On the other hand, systemic corticosteroids, which are considered first-line therapy for the management of DM, are not recommended for use in cases where psoriasis coexists with DM unless the situation is highly critical and the symptoms cannot be controlled by other therapies, due to concern regarding the potential exacerbation of psoriasis after corticosteroid withdrawal [33]. Adalimumab, a TNF-\(\alpha\) inhibitor, secukinumab, an IL-17 inhibitor, and ustekinumab, which targets interleukin IL-12/23p40, are effective treatments for psoriasis and have shown potential in treating psoriasis concomitant with DM. Nevertheless, secukinumab has been reported as a triggering factor for psoriasis concurrent with DM. This has led to caution in using biologics targeting the IL23-IL17 pathway to treat this condition. The medication targeting the type II IFN-mediated signaling pathway could be a therapeutic alternative for psoriasis concurrent with DM. The type II IFN-mediated signaling pathway is regulated by JAK 1 and JAK2, and there are several JAK inhibitors targeting this pathway, including tofacitinib, ruxolitinib, baricitinib, abrocitinib [48]. Recently, [PERSON] et al. reported a case of refractory psoriasis with DM demonstrating a positive response to oral upadacitinib, and the treatment was well tolerated.