Papillon-Lefèvre Syndrome Presenting with Early-Onset Psoriasis and Osteomyelitis

Background Papillon-Lefèvre syndrome (OMIM #245000) is a rare autosomal recessive genodermatosis caused by mutations in the cathepsin C gene (CTSC). CTSC encodes the lysosomal protease cathepsin C, which is highly expressed in white blood cells. Defects in CTSC typically lead to early-onset hyperkeratosis and periodontitis, resulting in premature tooth loss. Case Presentation We report the case of an 8-year-old boy with a history of early-onset psoriasis diagnosed in infancy, for which he has been receiving adalimumab 20 mg every other week. The patient presented to our clinic with complaints of swelling and pain in the right knee over the past few weeks, accompanied by intermittent fever that improved with paracetamol. On physical examination, a severe psoriatic rash was noted on the extremities (hands, feet, elbows, and knees), accompanied by dystrophic nails. Significant swelling and a flexion contracture of the right knee joint were observed. The patient was started on prednisolone (0.5 mg/kg PO) with a tapering plan over one month, methotrexate (7.5 mg SC weekly), and folic acid (1 mg PO daily). Despite this, the swelling worsened and fever persisted. He was subsequently admitted for further evaluation. Laboratory tests revealed a WBC count of 13.2, hemoglobin of 10.7, platelet count of 464, and ESR of 78. Ultrasound imaging identified two oval-shaped hypoechoic masses in the lower right thigh. MRI of the knee revealed a large collection surrounding the distal femur (Brodie abscess) with involvement of the growth plate and epiphysis, along with bone marrow edema suggestive of osteomyelitis. Blood cultures were negative; however, abscess fluid cultures grew methicillin-resistant Staphylococcus aureus. Whole-exome sequencing revealed a likely pathogenic homozygous variant in the CTSC gene (c.899G>A; p.Gly300Asp), consistent with a diagnosis of Papillon-Lefèvre syndrome. This variant has been reported in the literature as causative of Papillon-Lefèvre syndrome. Conclusion Early-onset, difficult-to-treat psoriasis should prompt a consideration of genetic testing, particularly in patients with a history of unusual infections. The management of Papillon-Lefèvre syndrome requires a multidisciplinary approach, involving pediatricians, dermatologists, immunologists, dentists, and surgical team. Early diagnosis provides an opportunity for aggressive management of periodontitis, potentially reducing the risk of premature tooth loss