Pruritus

Differential

Dermatologic disorders
- Xerosis
- Eczematous dermatitis
  - Atopic dermatitis
  - Contact dermatitis
- Urticaria
- Papulosquamous disorders
- Infections
  - Dermatophyte infections (tinea cruris, tinea pedis, tinea capitis)
  - Scabies
- Secondary skin disorders
  - Lichen simplex chronicus
  - Prurigo nodularis
- Scars
- Others: bullous pemphigoid, dermatitis herpetiformis, mastocytosis
- Systemic disorders
  - Chronic kidney disease, especially those on dialysis
  - Liver disease
    - Cholestatis pruritus from primary biliary cirrhosis, intrahepatic cholestasis of pregnancy, primary sclerosing cholangitis, viral hepatitis, drug-induced cholestasis, obstructive jaundice
  - Endocrine disorders
    - Thyrotoxicosis, especially with Graves disease, more commonly than hypothyroidism
    - Diabetes mellitus
  - Malignancy
    - Hodgkin lymphoma
    - Polycythemia vera
    - Mycosis fungoides
    - Other hematologic malignancies
    - Gastric carcinoid
  - Infections
    - Primary varicella
    - HIV
  - Rheumatic disorders, including dermatomyositis, systemic sclerosis, Sjögren syndrome
  - Drug reactions, including drug-induced dry skin from retinoids or phototoxicity from doxycycline
- Neuropathic itch
  - Brachioradial pruritus
  - Notalgia paresthetica
  - Postherpetic neuralgia
  - Multiple sclerosis
  - Other small fiber neuropathy
- Chronic pruritus of unknown origin
- Psychogenic itch, including psychogenic excoriation, delusional parasitosis, and substance use disorder

Investigations

CBC with differential, liver tests (bilirubin, ALT, ALP), TSH, creatinine
Consider chest x-ray