Cutaneous Signs of Internal Disease: "Dermadromes"

Introduction

Certain skin lesions are sentinels for internal pathology. The diagnosis here is not the skin lesion itself (which is often asymptomatic), but the systemic disease it heralds.

This chapter maps the Skin Sign to the required Internal Workup.

14.1 Paraneoplastic Screen (Cancer Signs)

These signs are statistical markers for underlying malignancy.

Skin Sign	Morphology	Associated Cancer	Workup Required
Acanthosis Nigricans (Malignant)	Rapid onset velvety hyperpigmentation (Palms/Soles - "Tripe Palms")	Gastric Adenocarcinoma	Endoscopy/Colonoscopy
Sign of Leser-Trélat	Explosive onset of Seborrheic Keratoses	GI Adenocarcinoma	Endoscopy/Colonoscopy
Dermatomyositis	Heliotrope Rash, Gottron's Papules	Ovarian, Lung, Breast	CT Chest/Abd/Pelvis, Age-appropriate screening
Necrolytic Migratory Erythema	Annular erosions on groin/face. Beefy tongue.	Glucagonoma (Pancreas)	CT Pancreas, Glucagon levels
Acrokeratosis Paraneoplastica (Bazex)	Hyperkeratosis of Ear helix, Nose, Fingers	Esophageal/Lung SCC	CT Chest, ENT exam
Sweet Syndrome	Tender, juicy red inflammatory plaques + Fever	AML (Leukemia)	CBD, Peripheral Smear

14.2 Diabetic Screen

Skin signs that suggest undiagnosed or uncontrolled Diabetes.

Necrobiosis Lipoidica:
- Sign: Yellow-brown, atrophic, waxy plaques on the shins. Telangiectasia visible.
- Implication: Strong diabetes association (though control doesn't improve the rash).
Acanthosis Nigricans (Benign):
- Sign: Velvety thickening of posterior neck/axillae.
- Implication: Insulin Resistance (Type 2 DM).
Scleredema Diabeticorum:
- Sign: Woody, non-pitting induration of the upper back/neck.
- Implication: Long-standing, poorly controlled diabetes.
Bullosis Diabeticorum:
- Sign: Spontaneous blistering on feet/legs without trauma.

14.3 Thyroid Screen

Pretibial Myxedema:
- Sign: Indurated, "orange-peel" plaque on shins.
- Implication: Graves' Disease (Hyperthyroid). Often associated with Ophthalmopathy.
Madarosis:
- Sign: Loss of the lateral 1/3 of the eyebrow.
- Implication: Hypothyroidism (Hertoghe's Sign).

14.4 Connective Tissue Disease Clues

Sign	Suggests	Specific Features
Malar Rash	SLE	Spares Nasolabial Folds (unlike Rosacea). Photodistibuted.
Heliotrope Rash	Dermatomyositis	Violaceous edema of eyelids.
Sclerodactyly	Scleroderma	Loss of finger skin folds. Unable to pinch skin.
Livedo Reticularis	Antiphospholipid	Net-like mottling on legs. Risk of thrombosis/stroke.
Palpable Purpura	Vasculitis	Non-blanching. Lower respiratory tract involvement? Kidney?

14.5 Sarcoidosis: Great Mimicker

Sarcoidosis can look like almost anything.

Lupus Pernio: Violaceous, infiltrated plaque on the Nose (beaded rim).
- Risk: Associated with chronic fibrotic lung disease and upper airway involvement.
Scar Sarcoidosis: Old scars (knees, tattoos) suddenly become red and infiltrated.
Papular Sarcoid: Brown-red papules on the face (apple-jelly on diascopy).

14.6 Diagnostic Algorithm: Patient with "Lumps"

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