Diffuse palmoplantar keratoderma with erythematous plaques develops between the first and fourth years of life, with the soles being usually more severely affected than the palms. Psoriasiform hyperkeratosis can overflow onto the dorsal surfaces of the hands and feet (transgredient spread) and, less frequently, lesions can be seen on the limbs (knees, elbows). Skin lesions are followed by intense gingivitis that rapidly progresses into periodontitis with alveolar bone lysis and early loss of primary dentition. The skin lesions are aggravated by cold and during episodes of severe periodontitis. During childhood, the phenomenon of periodontal disease recurs with rapid loss of permanent dentition. Cases of PLS with mild and/or late-onset periodontal disease have been reported occasionally. PLS is accompanied, in half of the patients, by enhanced susceptibility to cutaneous and systemic infections (furunculosis, skin abscesses, pyoderma, hidradenitis suppurativa, respiratory tract infection...). Patients may also present with malodorous hyperhidrosis, follicular hyperkeratosis, nail dystrophy or dural calcifications. The association of PLS with malignant melanoma or squamous cell carcinoma has been reported in very rare occasions.
PLS is due to mutations in the CTSC gene (11q14.2) that codes for cathepsin C (also known as dipeptidyl peptidase I), a lysosomal protease playing a role in epidermal differentiation and desquamation and in activation of serine proteases expressed in cells of the immune system. CTSC mutations lead to an almost total loss of cathepsin C activity which seems to result in susceptibility to specific virulent pathogens. It is also suggested that other immune-mediated deficiencies in the host defense mechanism could be involved in the pathogenesis of PLS.
