B9. Paraneoplastic skin disorders

Paraneoplastic syndrome refers to any sign or symptom which occurs due to hormone or cytokine production by tumour cells, or by the immune response to the malignancy. Generally, it's defined as any syndrome due to non-metastatic effects of the malignancy. Paraneoplastic syndromes are rare, occuring in somewhere from 2-20% of malignancies. They often develop before the cancer diagnosis.

It’s important to recognise these diseases because they can give earlier diagnosis of the tumour and because their prognosis is better the earlier the treatment is initiated.

Pathomechanism

There may be many underlying mechanisms. Tumour cells may produce hormones or cytokines which cause systemic or distant effects. Another mechanism is molecular mimicry, where the immune system T cells or antibodies directed against the tumour cells may mistakenly attack healthy cells.

Dermatology

Many dermatological paraneoplastic syndromes exist, but they are rare.

Acanthosis nigricans is normally a genetic disorder characterized by formation of grey-black patches on the skin, an asymmetric velvety thickening and hyperpigmentation of skin folds. Pruritus may also occur. In may occur often before the malignancy itself becomes symptomatic. It's most common in elderly

Leser-Trélat sign refers to the sudden appearance of many seborrheic keratoses, a form of common benign skin tumour. This is associated with solid cancers, especially GI malignancies.

Other possible dermatological paraneoplastic syndromes include:

• Dermatological disorders only seen as paraneoplastic syndromes (obligate paraneoplastic disorders)
  • Erythema gyratum repens
    • Adenocarcinoma
  • Acrodermatitis psoriasiformis
    • Upper airway cancer
  • Hypertrichosis acquisita
  • Acrokeratosis bazex/acrokeratosis paraneoplastica
    • Psoriasiform lesions
    • Upper airway or GI cancer
  • Paraneoplastic pemphigus
• Dermatological orders also seen without malignancies (facultative paraneoplastic disorders)
  • Pyoderma gangrenosum
    • Painful, rapidly progressive ulcerated lesions
    • Also in Crohn disease
  • Bullous pemphigoid
  • Dermatomyositis
  • Sweet syndrome
    • Painful erythematous papules, plaques, nodules
  • Generalised herpes zoster (due to immune system depression)
  • Generalized acquired ichthyosis