Case Presentation: A 72 year old diabetic male presents to the hospital with a severe and extensive rash involving the entire body. Despite being treated with prednisone, topical steroids and doxycycline, the patient’s symptoms worsened and spread cephalocaudally, eventually spreading to the hands and bilateral lower extremities. Skin biopsy confirmed a diagnosis of Pityriasis Rubra Pilaris. While inpatient, the patient was treated with Prednisone Acitretin along with topical triamcinolone and hydrocortisone. He was also started on Ixekizumab (Taltz) injection with subsequent improvement in symptoms. The patient was discharged on daily Acitretin and intermittent Taltz injections every other week.
Discussion: Pityriasis rubra pilaris (PRP) is a rare inflammatory skin disorder characterized by follicular, hyperkeratotic papules, well-demarcated plaques with varying degrees of scale and erythroderma with islands of sparing. The etiology of PRP is idiopathic, but some cases have been reported to be triggered by medications. In this case, the patient’s onset of symptoms aligned with starting Losartan; while no prior cases of Losartan-induced PRP have been reported, other dermatological side-effects of Losartan, such as psoriasis and erythroderma, have been. Based on the Naranjo Adverse Drug Reaction Probability Scale and the chronicity of symptom onset, it is possible that the onset of PRP was a result of adding Losartan. Although pathogenesis of PRP is not fully understood, it is speculated that the IL-23/Th17 axis may play an important role, as PRP has been shown to respond to therapies targeting IL-17 and IL-23. This case supports this hypothesis as the patient’s condition improved following the administration of Ixekizumab, an anti-IL-17 monoclonal antibody. While PRP sometimes spontaneously resolve, symptoms are often present for years, causing both functional and psychosocial impairment and necessitating initiation of treatment. With the improvement of symptoms, the patient expressed subjective improvement in their mood and quality of life, which they reported was declining since the onset of their symptoms.
Conclusions: It is important to be aware of potential rare or atypical conditions such as Pityriasis Rubra Pilaris when prescribing medications with known dermatological side-effects such as Losartan. Treatment with anti-IL-17A monoclonal antibodies, in combination with an oral retinoid, showed improvement of symptoms in this case of Pityriasis Rubra Pilaris.While the condition may be self-limiting, early treatment of symptoms of PRP proved to be important for the patient’s quality of life and mental health.
