Chief Complaint: Pruritus
Here’s a clear, structured way to determine the cause of itching (pruritus), integrating what we know from dermatology and internal medicine. I’ll give you a diagnostic algorithm, then the major etiologic categories, and finally the red flags that push you toward systemic disease.
This single question immediately narrows the differential.
This usually points to primary skin disease, infestation, or allergic/irritant reactions.
Use the rash pattern to guide you:
| Rash Pattern | Likely Causes |
|---|---|
| Eczematous patches/lichenification | Atopic dermatitis, contact dermatitis American Academy of Dermatology |
| Wheals (hives) | Urticaria (allergic, idiopathic) |
| Burrows, papules in finger webs, wrists | Scabies American Academy of Dermatology |
| Circular scaly plaques | Tinea (ringworm) |
| Greasy scales on scalp/face | Seborrheic dermatitis |
| Vesicles on erythematous base | Shingles (dermatomal) |
| Follicular pustules | Folliculitis |
Ask about:
This is where your internal‑medicine instincts shine.
When the skin looks normal, think systemic disease, neuropathic itch, or medication effects.
These are well‑documented causes of generalized pruritus:
| Disease Category | Clues | Notes |
|---|---|---|
| Liver disease (cholestasis) | Itch starts on palms/soles, worse at night | Seen in hepatitis C, cirrhosis, obstructed bile duct American Academy of Dermatology |
| Kidney disease | Dry, scaly skin; intense nocturnal itch | Common in advanced CKD/dialysis patients American Academy of Dermatology |
| Hematologic disease | Hodgkin lymphoma (classically severe), polycythemia vera | Itch may be the only symptom American Academy of Dermatology |
| Thyroid disease | Dry skin (hypothyroid) or diffuse rash (hyperthyroid) | Cleveland Clinic |
| Diabetes | Localized neuropathic itch (hands, feet, legs) | Cleveland Clinic |
| HIV | Generalized pruritus with or without rash |
Think of:
Common culprits:
Order when itching is generalized, chronic, or unexplained:
If scabies, fungal infection, or lice are suspected.
If allergic contact dermatitis is suspected.
Only if systemic red flags (lymphadenopathy, B symptoms).
Seek deeper evaluation if:
You can think of pruritus as a three‑branch algorithm:
ITCH | ----------------------- | | Rash present? No rash present? | | Dermatologic → Systemic / Neuropathic / Allergic / Medication-related Infectious
Then refine using:
This approach mirrors the diagnostic logic used in internal medicine and dermatology and aligns beautifully with your pattern‑recognition style.
If you want, I can also build you a one‑page master algorithm for pruritus that you can use for boards or clinical practice.
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Here’s how I’d walk through this one with you, Silverio — this is classic board‑style scabies.
Everything about this vignette is screaming scabies:
This is the exact distribution and symptom pattern the boards love.
You do not need to confirm with skin scrapings unless the diagnosis is uncertain. In a classic presentation like this, treatment is the correct next step.
If you want, I can turn this into a quick scabies diagnostic/treatment algorithm — fits perfectly with your love for structured reasoning.
| History or Physical Exam | Hyperemia of the Skin |
Differential Diagnosis
Contact Dermatitis: This can be caused by contact with allergens or irritants, resulting in redness and itching.
Atopic Dermatitis (Eczema): A chronic inflammatory skin condition characterized by itching, redness, and sometimes oozing or crusting.
Urticaria (Hives): Raised, itchy welts on the skin that are often accompanied by redness and can be triggered by various factors, including allergens.
Psoriasis: An autoimmune skin condition characterized by red, scaly patches of skin that may itch and burn.
Scabies: An infestation of mites that burrow into the skin, causing intense itching and redness.
Fungal Infections: Conditions like ringworm or candidiasis can cause red, itchy skin.
Allergic Reactions: Allergies to medications, foods, or insect stings can lead to generalized itching and skin redness.
Insect Bites or Stings: Mosquito bites, bee stings, or other insect bites can cause localized itching and redness.
Drug Reactions: Some medications can cause skin reactions, such as drug-induced hypersensitivity syndrome (DIHS) or Stevens-Johnson syndrome.
Scaly Skin Disorders: Conditions like pityriasis rosea or nummular eczema can cause itchy, red, scaly patches of skin.
Dermatitis Herpetiformis: A skin manifestation of celiac disease, causing intensely itchy, red, blistering lesions.
Autoimmune Skin Diseases: Conditions like lupus or dermatomyositis can cause skin rashes, redness, and itching.
Inflammatory Skin Conditions: Conditions like lichen planus or granuloma annulare can cause red, itchy plaques on the skin.
Parasitic Infections: Infections like cutaneous larva migrans or hookworm infections can cause skin irritation, redness, and itching.
Neurological Causes: In some cases, neurological disorders can cause itching without an obvious skin rash.
Systemic Causes: Underlying systemic conditions like liver disease, kidney disease, or thyroid disorders can manifest with skin symptoms, including itching and redness.
| Next Pivotal Assessment | Finding |
|---|---|
Furher History or Physical Exam
|