INTRODUCTION
Pityriasis lichenoides is a scarce cutaneous disorder with unknown etiology. It contains a range of clinical manifestations including acute papular lesions that quickly grow into pseudo vesicles and central necrosis to small, scaling, benign-appearing papules.1,2 The tumor necrosis factor (TNF) cytokines superfamily contain a group of pro-inflammatory cytokines that activate cellular differentiation signaling pathways.3,4 Etanercept, a TNF-α inhibitor is applied as single treatment or in addition to other immunosuppressants (such as methotrexate) to treat specific inflammatory diseases. This study presents a 38-year-old man with ankylosing spondylitis (AS) who developed pityriasis lichenoides chronica (PLC) while on etanercept treatment.
CASE PRESENTATION
A 38-year-old male with back pain came to our outpatient clinic. He was started on NSAIDs on demand. Three years afterwards, polyarthritis and tenosynovitis in the knees, hands, and feet was developed. He was referred to a rheumatologist and he was found to be HLA-B27 positive, and pelvic radiographs showed bilateral grade 2 sacroiliitis. The Schober's test was positive and magnetic resonance imaging (MRI) showed the sacroiliac joint inflammation. He was diagnosed with AS. Complete blood count, blood sugar, renal function tests, liver function tests, and urine routine were all within normal limits. Thyroid function was also normal. Psychiatric examination of the patient was unremarkable. There was no personal or familial history of arthritis. The patient did not present any comorbidity. Due to inefficacy of NSAIDs, etanercept 50 mg per week subcutaneously was prescribed. After eight weeks, he was evaluated by a dermatologist for the appearance of scaly erythematous papules, on the back and arms. A diagnosis of PLC was made (Figure 1,2). Treatment with daily topical corticosteroids was initiated. After one month, the rash subsided and etanercept was continued for the patient.
DISCUSSION
Pityriasis lichenoides is an uncommon, idiopathic, acquired disease, characterized by groups of scaly erythematous papules that might persist for a long time. It is diagnosed by its appearance and clinical history and usually confirmed by histopathological examination. The span of the disease includes comparatively mild chronic to a further severe acute eruption form. The mild chronic subtype, known as PLC is characterized by the slow development of small, scaling papules that spontaneously flatten and regress over a short period of time. In other pityriasis lichenoides spectrum the acute form known as pityriasis lichenoides et varioliformis acuta (PLEVA) exists, consist of abrupt eruption of minor scaling papules that progress into
