Paraneoplastic Dermatoses

Acanthosis nigricans

•    Velvety hyperpigmented plaques, most often in flexures (axillae, neck, groin)

•    Common in insulin resistance (benign form)

•    Sudden onset and extensive distribution → strong association with GI adenocarcinomas, especially gastric cancer

Dermatomyositis

•    Heliotrope rash, Gottron’s papules, periungual telangiectasia

•    Proximal muscle weakness

•    In adults >50, associated with underlying malignancy:

o    Ovarian (especially in women)

o    Lung

o    Colorectal

o    Pancreatic

Necrolytic migratory erythema

•    Erythematous, annular, blistering lesions with central clearing; affects perineum, groin, lower abdomen

•    Strongly associated with glucagonoma (α-cell tumour of pancreas)

•    Often accompanied by diabetes mellitus, weight loss, and glossitis

Genodermatoses Associated with Malignancy

Neurofibromatosis type 1 (NF1)

•    Café-au-lait spots (≥6, >5 mm prepubertal, >15 mm postpubertal)

•    Lisch nodules (iris hamartomas)

•    Neurofibromas (cutaneous and plexiform)

•    Increased risk of:

o    Optic gliomas

o    Phaeochromocytomas

o    MPNST (malignant peripheral nerve sheath tumours)

Tuberous sclerosis

•    Facial angiofibromas (adenoma sebaceum)

•    Shagreen patches (connective tissue nevus, often lower back)

•    Ash-leaf macules (hypopigmented, Wood’s lamp aids detection)

•    Periungual fibromas (Koenen’s tumours)

•    Associated tumours:

o    Renal angiomyolipomas

o    Cardiac rhabdomyomas

o    Subependymal giant cell astrocytomas

Peutz–Jeghers syndrome

•    Mucocutaneous pigmentation (lips, oral mucosa, perioral area)

•    Multiple hamartomatous GI polyps

•    Increased risk of:

o    GI cancers (colorectal, pancreatic, gastric, small bowel)

o    Breast, ovarian, cervical cancers

Sign of Leser–Trélat

•    Sudden onset of multiple, eruptive seborrhoeic keratoses

•    Often pruritic

•    Suggests underlying internal malignancy, commonly:

o    GI adenocarcinomas (especially stomach)

o    Less commonly lymphomas

Extra Revision Pearls

•    New-onset, rapidly spreading acanthosis nigricans → always consider gastric adenocarcinoma

•    NF1 vs NF2:

o    NF1: cutaneous signs, optic gliomas

o    NF2: bilateral vestibular schwannomas, minimal skin signs

•    Necrolytic migratory erythema: classic "ring-shaped" migrating plaques → think glucagonoma

•    Leser–Trélat sign: don’t confuse with benign slow-growing seborrhoeic keratoses