Pruritus

Differential Diagnosis

• Dermatologic disorders
  • Xerosis
  • Eczematous dermatitis
    • Atopic dermatitis
    • Contact dermatitis
  • Urticaria
  • Papulosquamous disorders
    • Psoriasis
    • Lichen planus
    • Pityriasis rubra pilaris
  • 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