IMPORTANCE: Treatment of pityriasis rubra pilaris (PRP) is solely based on its 
resemblance to psoriasis rather than any knowledge of its pathomechanism. 
Insight into pathogenic mediators of inflammation is essential for targeted and 
valid treatment options that could replace previous serendipitous therapeutic 
approaches in refractory PRP.
OBJECTIVE: To determine whether blockade of the interleukin 23-helper T cell 17 
(IL-23-TH17) pathway with ustekinumab represents an efficacious and, based on 
its proinflammatory cytokine profile, targeted treatment option in PRP.
DESIGN, SETTING, AND PARTICIPANTS: In this case report, a patient with PRP 
received outpatient treatment at a university hospital department of dermatology 
with ustekinumab according to the dosing regimen approved for psoriasis. 
Lesional skin biopsy samples were taken from this patient and 2 others with 
refractory PRP. Messenger RNA (mRNA) expression of proinflammatory innate and 
T-cell-derived cytokines were measured and compared with skin samples from 
patients with psoriasis and healthy donors. From 1 patient, lesional skin 
samples were taken before ustekinumab treatment and 4 and 28 weeks after 
treatment initiation. Follow-up was completed after 6 months.
INTERVENTION: Subcutaneous ustekinumab, 45 mg, at weeks 0 and 4 and quarterly 
thereafter.
MAIN OUTCOMES AND MEASURES: The primary outcome was to determine the changes in 
expression of proinflammatory innate and T-cell-derived cytokines during 
ustekinumab therapy. The secondary objective was to evaluate the clinical and 
histopathologic phenotype in relation to the mRNA expression profile of 
proinflammatory cytokines.
RESULTS: In lesional PRP skin samples from a single patient, upregulated 
expression levels were found for most proinflammatory innate cytokines, 
including tumor necrosis factor (TNF), IL-6, IL-12, IL-23, and IL-1β. Among 
adaptive T-cell cytokines, an increase of TH1 cytokines and, in particular, TH17 
cytokines IL-17A, IL-17F, and IL-22 was seen in PRP. The patient with PRP who 
received ustekinumab showed regression of skin lesions after 2 weeks and almost 
complete resolution after 1 month. Clinical and histopathologic improvement 
paralleled the expression levels of TH17 cytokines but not of interferon-γ and 
TNF, which lagged behind the amelioration.
CONCLUSIONS AND RELEVANCE: In this case report, a role of the IL-23-TH17-axis in 
PRP was identified, suggesting a shared pathogenic inflammatory pathway with 
psoriasis, despite evident clinical and histopathologic differences. In 
addition, this report provides a rationale for targeting the IL-23-TH17-pathway 
as a treatment option for refractory PRP.