Acrokeratosis paraneoplastica (Bazex syndrome).

Acrokeratosis paraneoplastica of Bazex (APB) is a paraneoplastic dermatosis heralding an underlying malignancy, most commonly squamous cell carcinoma of the upper aerodigestive tract. The syndrome is characterized by psoriasiform, violaceous, scaly plaques localized to acral areas and the ears and nose. Involvement of the nails, helical rim, and nasal tip are also common. Histologically, APB demonstrates spongiosis, interface dermatitis, and lichenoid inflammation, with direct immunofluorescence revealing variable deposits of immunoglobulins and complement along the basement membrane. Although the pathophysiology of APB is unclear, proposed mechanisms include tumor-derived factors, immune-mediated processes, and metabolic deficiencies. Recognizing this syndrome's distinctive cutaneous findings is essential for early cancer detection, as these manifestations often precede the diagnosis of malignancy by months. Management focuses on treating the underlying malignancy, with cutaneous lesions typically resolving upon successful cancer therapy. Symptomatic relief may be achieved with topical or systemic treatments, although these do not address the primary cause.