Focal Synovial Inflammation Versus Enthesitis Theory in Distal Psoriatic Arthritis: A Pioneer Histopathologic Study

Are There Signs of Enthesitis in Nail Psoriasis? An Immunohistological Study of Nail Psoriasis With and Without Psoriatic Arthritis

ABSTRACT

The concept of nail psoriasis as an entheseal-driven disease has essentially been formulated on the basis of radiological findings because it is usually not possible to obtain the tissue directly from the joints. The aim of this retrospective study was to evaluate the histological features of isolated nail psoriasis with and without distal interphalangeal psoriatic arthritis (PsA), focusing on the question as to whether the fascia and adipose tissue surrounding the apex of the nail unit genuinely show an inflammatory infiltrate. In support of the nail-enthesitis theory, an ongoing inflammatory infiltrate could be expected. An immunohistochemical study was performed to evaluate the distribution and phenotype of the inflammatory infiltrate in nail psoriasis with and without PsA. This study did not show an inflammatory infiltrate in the fascia connecting the nail to the extensor tendon. CD8 and CD4 subsets were present in equal number in the nail dermis of nail psoriasis with or without PsA, which is a similar distribution to that seen in psoriatic synovium while skin psoriasis is characterized by a dermal predominance of CD4 T lymphocytes. Because of this study and recent microanatomic studies of the normal nail unit, it is possible to move away from a purely anatomic explanation of the strong association between nail psoriasis and PsA and to propose immunological factors as contributory. This study provides support for the hypothesis that CD8+ T cells play a crucial role in the pathogenesis of nail psoriasis through a pathogenic pathway similar to that of PsA and contrasting with that of the skin.

Translational Research Studies Unraveling the Origins of Psoriatic Arthritis: Moving Beyond Skin and Joints

Patients with psoriatic arthritis (PsA) are suffering from a decreased quality of life despite currently available treatments. In the latest years, novel therapies targeting the IL-17/IL-23 and TNF pathways improved clinical outcome. Despite this, remission of disease is not achieved in a considerable group of patients, continuous treatment is very often required to reach clinical remission, and prevention of PsA in patients with psoriasis (PsO) is currently impossible. A better understanding of PsA pathogenesis is required to develop novel treatment strategies that target inflammation and destruction more effectively and at an early stage of the disease, or even before clinically manifest disease. The skin is considered as one of the sites of onset of immune activation, triggering the inflammatory cascade in PsA. PsO develops into PsA in 30% of the PsO patients. Influenced by environmental and genetic factors, the inflammatory process in the skin, entheses, and/or gut may evolve into synovial tissue inflammation, characterized by influx of immune cells. The exact role of the innate and adaptive immune cells in disease pathogenesis is not completely known. The involvement of activated IL-17A+ T cells could implicate early immunomodulatory events generated in lymphoid organs thereby shaping the pathogenic inflammatory response leading to disease. In this perspective article, we provide the reader with an overview of the current literature regarding the immunological changes observed during the earliest stages of PsA. Moreover, we will postulate future areas of translational research aimed at increasing our knowledge on the molecular mechanisms driving disease development, which will aid the identification of novel potential therapeutic targets to limit the progression of PsA.