Very itchy skin. Differential diagnosis

Author: Hon A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand, May 2016.


Itch is defined by a desire to scratch.  

An acute or chronic itchy rash is most often due to dermatitis/eczema. Dermatitis can be primary, or secondary to scratching.

Stages include:

Acute dermatitis

Acute dermatitis

Subacute dermatitis

Subacute dermatitis

Chronic dermatitis

Chronic dermatitis

Infected dermatitis

Infected dermatitis

If clinical diagnosis of an itchy skin problem is uncertain, consider performing the following tests:

Dermatoscopic examination of hair shaft

Dermatoscopic examination of hair shaft

  • Dermatoscopic examination of possible burrows, if hands affected 
Dermatoscopic examination of possible burrows

Dermatoscopic examination of possible burrows

  • Swab for bacterial and viral culture if pustules, crusting

Skin biopsy for histopathology, and if available, direct immunofluorescence 

Skin biopsy for histopathology

Skin biopsy for histopathology

  • If itch is generalised and no primary skin rash observed, check blood count, iron studies, renal, liver and thyroid function, chest X-ray

General treatments for itchy skin conditions may include:

Differential diagnosis

Consider:

  • Is the itch localised or generalised? What is its distribution
  • Is there a primary rash or not?
  • Erosions, crusting, bruising and infection can be due to excoriation and are of no help diagnostically.

Very itchy skin with localised rash   

  1. Contact dermatitis 
  • Site depends on cause
  • Irritant > allergen
  • Asymmetrical, odd shapes
  • Often intermittent
Contact dermatitis

Contact dermatitis

    • Egg cases close to scalp
    • Blood spots behind ears
Head lice

Head lice

Insect bites

Insect bites

  • Lichen planus 
    • May be localised to any site
    • Grouped firm polygonal violaceous plaques
    • Biopsy confirmatory
Lichen planus

Lichen planus

  • Lichen sclerosus
    • Vulva > penis > elsewhere
    • White dry skin
    • Sometimes, purpura, blisters, resorption, scarring    
    • Biopsy confirmatory
Lichen sclerosus

Lichen sclerosus

  • Lichen simplex 
    • Localised lichenification
    • Common sites: wrist, ankle, neck, genitals
    • Sometimes bilateral
Lichen simplex

Lichen simplex

  • Pompholyx 
    • Crops of vesicles along fingers, toes, palms, soles
Dyshidrotic eczema

Dyshidrotic eczema

  • Venous dermatitis 
    • Affects one ankle initially then may spread to other leg and can generalise (autoeczematisation)
    • Signs of venous disease: hardened, narrowed ankle (lipodermatosclerosis), orange-brown discolouration (haemosiderin)
    • +/- Varicose veins 
Venous dermatitis

Venous dermatitis

Mildly itch skin with localised rash  

Asteatotic eczema

Asteatotic eczema

  • Psoriasis 
    • Itch is sometimes severe
    • Localised variant affects s­calp, elbows, knees; or palms and soles   
Psoriasis

Psoriasis

  • Seborrhoeic dermatitis 
    • In and around hair-bearing scalp, eyebrows, hairy chest
    • Skin folds behind ears, nasolabial fold, axilla
    • Salmon pink, flaky
Seborrhoeic dermatitis

Seborrhoeic dermatitis

Very itchy skin with generalised rash

Autoeczematisation

Autoeczematisation

  • Bullous pemphigoid 
    • Elderly, especially with brain injury
    • May start like eczema or urticaria
    • Large blisters
    • Biopsy confirmatory
Bullous pemphigoid

Bullous pemphigoid

Dermatitis herpetiformis

Dermatitis herpetiformis

Eczema

Eczema

Discoid eczema

Discoid eczema

Erythroderma

Erythroderma

  • Lichen planus 
    • Skin +/- mucosal surfaces
    • Grouped firm polygonal violaceous plaques on wrists, shins, lower back
    • Lacy white pattern in buccal mucosa
    • Painful erosions on tongue, vulva, vagina, penis
    • Biopsy confirmatory
Lichen planus

Lichen planus

  • Mycosis fungoides 
    • Slowly evolving slightly scaly annular and roundish patches, plaques and sometimes nodules
    • Various morphologies
    • Buttocks, breasts common initial sites
    • Biopsy confirmatory
T-cell lymphoma

T-cell lymphoma

Neurodermatitis

Neurodermatitis

Nodular prurigo

Nodular prurigo

  • Scabies
    • Burrows between fingers, wrist creases
    • May be secondarily infected
    • Papules in axillae, groin, penis
    • Polymorphous rash on trunk
    • Scale-crust between fingers, elbows, scalp in elderly or immune suppressed
Scabies

Scabies

Transient acantholytic dermatosis

Transient acantholytic dermatosis

  • Urticaria 
    • Acute < 6 weeks
    • Chronic > 6 weeks
    • Spontaneous or inducible weals
    • No blisters or dryness or scale
    • Scratch skin to elicit linear weal in dermographism
Urticaria

Urticaria

Mildly itchy skin with generalised rash

  • Psoriasis  
    • Itch is sometimes severe
    • Symmetrical well-circumscribed plaques with silvery scale
    • Generalised large or small plaques
Psoriasis

Psoriasis

Xerotic eczema

Xerotic eczema

Localised itchy skin without rash

May have secondary lesions due to scratching:  erosions, purpura, lichen simplex and secondary infection.

Localised itch is often neuropathic/neurogenic. If scalp itchy, look carefully for head lice and their egg cases.

Excoriations

Excoriations

Lichen simplex

Lichen simplex

Lichen simplex

Lichen simplex

Generalised itchy skin without rash

Examine carefully for scabetic burrows.

Pruritus of pregnancy

Pruritus of pregnancy

 

Chronic renal insufficiency

Chronic renal insufficiency

    • Cholestasis
    • Iron deficiency
    • Polycythaemia vera
    • Hyperthyroidism
    • Lymphoma
    • Diabetic neuropathy
    • Drug-induced (eg opioid, vancomycin flushing)
    • Unknown origin 
Unknown origin

Unknown origin