The patient was a 31-year-old homosexual Chinese male with a 6-year history of multiple erythematous scaly plaques. Since June 2016, he has developed erythema, papules, plaques, and scales of various sizes throughout his body. Four months later, the rash increased rapidly, diffusing erythema all over the body, accompanied by a fever. He does not have a regular homosexual partners (regular homosexual partners), with some breaching the safe sex measures. The patient visited with the history of type 2 diabetes and penicillin allergy but no family history of psoriasis. A typical psoriatic rash covered over 90% of his body surface area, and he was admitted to the hospital with "erythrodermic psoriasis". Erythrodermic psoriasis was diagnosed in the context of the pathological examination and clinical features during hospitalization. The pathological manifestations indicated hyperkeratosis, confluent parakeratosis, Munro microabscesses, acanthosis hypertrophy, regular elongation of the rete ridges, papillary dermal edema, mildly dilated blood vessels, scattered perivascular lymphocytes, and neutrophils infiltrated around the upper epidermis and superficial dermis (Figure 1), which are typical characteristics of erythrodermic psoriasis. Simultaneously, the patient tested positive for the human immunodeficiency virus (HIV) antibody. The CD4+ T lymphocyte count was 28 cells/muL, and the HIV viral load was 5.05 x 104 IU/mL. The diagnosis was "HIV infection". The psoriasis was treated successively for 3 weeks with acitretin capsules, total glucosides of peony capsules, compound glycyrrhizin tablets, topical glucocorticoid cream, and moisturizers, and the condition was controlled. Oral tenofovir 200 mg once a day, 100 mg of oral lamivudine once a day, and 50 mg of oral lopinavir and ritonavir tablets twice a day were administered for continuous anti-HIV treatment, and the laboratory indicators were reviewed every six months. The re-examination results on December 11, 2019, showed that the CD4+ T cell count was greater than 200 cells/muL and the viral load was less than 100 IU/mL. During the period from November 2016 to March 2020, the patient took acitretin capsules orally for a long time for maintenance treatment. With the prolongation of the use time of acitretin A capsule, its efficacy gradually declined. The recurrence of psoriasis increased. 
In March 2020, the psoriasis rash recurred and aggravated, accompanied by noticeable pain in the cervical spine and sacroiliac joints, with unfavorable flexion, extension and rotation. On April 8, 2020, the results of the spine and hip joint MRI performed in another hospital (Figure 2A) suggested abnormal changes in the bilateral sacroiliac and hip joints, slight swelling of the surrounding soft tissue, and right external obturator muscle swelling. Sacroiliitis was considered. On May 5, 2020, he was admitted to our hospital again and diagnosed with psoriatic arthritis (involvement of axial joints) and psoriasis vulgaris (Figure 2B). Laboratory data revealed an CD4+ T lymphocyte number of 278 cells/muL, HIV viral load was less than 100 IU/mL, the eosinophil number of 0x109/L , the red blood cell number of 2.66x1012/L , the level of hemoglobin was 101 g/l , the C-reactive protein level was 33.91 mg/l , the erythrocyte sedimentation rate was 138.00 mm/h , with negative serologic examination for hepatitis A virus, hepatitis B virus, hepatitis C virus, and syphilis. The remaining hematological, biochemical investigations and urine analysis were in the normal ranges. Pre-treatment screening was negative for tuberculosis, including chest X-rays, an interferon-gamma release assay, whereas the Echocardiography (ECG) showed sinus arrhythmia. The psoriasis area and severity index (PASI) score of the skin lesion was 14.4 (Figure 3A), and the Disease Activity Index for Psoriatic Arthritis (DAPSA) score was 52. On May 7, 2020, after the patient was fully informed and signed the informed consent form, subcutaneous injections of 25 mg of etanercept twice weekly combined with 20 mg of acitretin capsules per day were administered. After three weeks, erythema and scales were significantly ameliorated (Figure 3B). After four weeks, the joint symptoms had almost subsided, and the DAPSA score was 0. Acitretin capsules were discontinued, and subcutaneous injection of 25 mg etanercept twice weekly was continued. The rash largely resolved after 21 weeks (Figure 3C), and the PASI score was 1.4. Subsequently, the etanercept dose was modified to a subcutaneous injection of 25 mg once weekly for eight weeks and once every two weeks for another eight weeks. The patient spontaneously discontinued etanercept treatment in February 2021. After 2 months, the rash recurred and worsened (Figure 4A). The PASI score was 20.2, and mild pain was observed in the cervical spine and spinal joints. The DAPSA score was 34, CD4+ lymphocyte count was 353 cells/muL, and HIV viral load was less than 100 IU/mL. On May 31, 2021, after repeatedly excluding any abnormalities in the examinations for the administration of biologics, secukinumab 300 mg was prescribed for treatment in the 0th, 1st, 2nd, 3rd, and 4th weeks in the context of anti-HIV treatment. Subsequently, it was administered at a dose of 300 mg every four weeks. After four weeks, the patient's joint symptoms completely disappeared, and the DAPSA score was 0. The times to achieve PASI 40, PASI 75, PASI 90, and PASI 100 were 2 weeks (Figure 4B), 4 weeks, 8 weeks (Figure 4C), and 29 weeks (Figure 4D), respectively. At present, secukinumab has been maintained for 1 year, and the clinical symptoms of psoriasis have stabilized (Figure 4E and the specific treatment timeline is shown in Figure 5). The CD4+ T lymphocyte count was 327 cells/muL, and the HIV viral load was less than 100 IU/mL. The results of the spine and hip joint MRI on April 25, 2022, indicated straightened physiological curvature of the cervical spine compared with the MRI results on April 8, 2020, before the use of biologics, with no abnormalities in height and signal of the vertebral body and less severe bilateral sacroiliac joint inflammation.    
The patient provided written informed permission to have any accompanying photos and case details published. The Hospital Ethics Committees of Dermatology Hospital of Jiangxi Province approved to publish the case details.