Acrokeratosis paraneoplastica, also known as acrokeratosis paraneoplastica of Bazex and Bazex syndrome, is a paraneoplastic dermatosis that occurs most often in association with squamous cell carcinomas involving the upper respiratory or digestive tracts. It was first described by Dr. Bazex, a French dermatologist in 1965. The nails, invariably, are involved and are typically the earliest manifestation of the condition. Nail changes include onycholysis, subungual debris, and horizontal or vertical ridging.

Nail involvement occurs in more than half of patients with Bazex syndrome. The nail changes may precede the diagnosis of the malignancy, disappear with its treatment, and reappear with its recurrence. However, in contrast to skin lesions, nail involvement may not always clear totally with treatment of the tumor.

Acrokeratosis paraneoplastica is characterized by scaly, erythematous plaques of the palms and soles as well as other acral sites including the ears, nose, and cheeks. Besides upper aerodigestive tract squamous cell carcinoma, acrokeratosis paraneoplastica may also be seen in association with lymphomas, multiple myeloma, neuroendocrine tumors, small cell lung cancer, adenocarcinoma of the lung, hepatocellular carcinoma, thymus cancer, cutaneous squamous cell carcinoma, gastric or esophageal adenocarcinoma, and genitourinary cancers.

Men of Northern European descent in their 40s are most often affected, and women are rarely affected.

The pathogenesis of Bazex syndrome is not completely understood, but an immunological mechanism has been suggested based on the histopathological findings of immunoglobulins and complement deposited along the basement membrane of skin of Bazex syndrome patients.