LAUSR

Dear Editor, We report on a 40-year-old man with psoriatic nail dystrophy and psoriatic arthritis who had an excellent clinical response to the anti-interleukin-23 (IL-23) monoclonal antibody tildrakizumab. His past medical history included bipolar disorder, asthma, and long-standing lumbar back pain following an injury. His regular medications included carbamazepine, lithium, sertraline, ziprasidone, budesonide/formoterol, and metformin. In 2016, he was diagnosed with left first toe osteomyelitis requiring surgical debridement, including removal of the nail bed, followed by a 3-month course of antibiotics. When the nail regrew it had an unusual appearance that was initially diagnosed as onychomycosis, however, nail scrapings revealed no evidence of fungal infection and a trial of systemic antifungal therapy and nail lacquer was ineffective. One year later, he developed abnormalities in the left second fingernail and left fourth toenail. Shortly after this, he developed an asymmetrical polyarthritis and was referred to a rheumatologist. Examination revealed synovitis of the left second distal interphalangeal (DIP) joint, right second metacarpophalangeal (MCP) joint, right ankle, right second and third and left second metatarsophalangeal (MTP) joints. Radiographs of his hands and feet revealed a solitary erosion of the left second DIP joint. Serum rheumatoid factor was negative, supporting a diagnosis of psoriatic arthritis. Treatment was commenced with methotrexate 20 mg weekly and folic acid 10 mg weekly. After 4 months of treatment, methotrexate was replaced by sulfasalazine 1 g twice daily, due to ongoing synovitis. He then presented to a dermatologist for management of his nail dystrophy. Examination revealed significant onycholysis, proximal onychomadesis and oil drop changes to the left second fingernail, onychauxis of the left fourth toenail and pitting of multiple other nails, consistent with psoriatic nail disease. Monthly triamcinolone acetonide injections were administered to the affected nails in addition to clobetasol dipropionate 0.05% ointment. After 7 months on this treatment regimen, there was minimal clinical improvement. His psoriatic arthritis remained active and methotrexate 20 mg weekly was restarted. This patient did not meet eligibility criteria for biologic therapy for psoriatic arthritis on the Australian Pharmaceutical Benefits Scheme (PBS) due to his low C-reactive protein (CRP) level of 5 and low joint count while taking treatment with methotrexate and sulfasalazine. Tildrakizumab was obtained through special-access scheme approval from the Australian Therapeutic Goods Administration (TGA). Screening investigations, including viral hepatitis serology and Quantiferon-TB Gold, were negative. Tildrakizumab 100 mg was administered subcutaneously at weeks 0 and 4. Twelve weeks later, when he presented for his third dose of tildrakizumab, there had been significant improvement in his nail dystrophy (Figures 1 and 2) and arthritis. The patient recorded the time taken for his pain to ease in the morning after waking during the first 9 weeks of tildrakizumab treatment. There was an overall reduction in the time taken for pain to ease in the affected joints (Table 1). He reported no adverse effects. Tildrakizumab is a humanized monoclonal antibody that inhibits the p19 subunit of IL-23 and is currently approved by the TGA, Food