Lichen planus

1. Lichen planus is a chronic inflammatory skin condition affecting the skin and mucosal surfaces. 
2. There are several clinical types of lichen planus that share similar features on histopathology.
   1. Cutaneous lichen planus
   2. Mucosal lichen planus
   3. Lichen planopilaris
   4. Lichen planus of the nails
   5. Lichen planus pigmentosus
   6. Lichenoid drug eruption

Causes:

• Lichen planus is a T cell-mediated autoimmune disorder, in which inflammatory cells attack an unknown protein within the skin and mucosal keratinocytes.
• Contributing factors to lichen planus may include:
  • Genetic predisposition
  • Physical and emotional stress
  • Injury to the skin; lichen planus often appears where the skin has been scratched or after surgery — this is called the isomorphic response (koebnerisation)
  • Localised skin disease such as herpes zoster—isotopic response
  • Systemic viral infection, such as hepatitis C (which might modify self-antigens on the surface of basal keratinocytes)
  • Contact allergy, such as to metal fillings in oral lichen planus (rare)
  • Drugs; gold, quinine, quinidine and others can cause a lichenoid rash.

characterised by 

• 4Ps—papule, purple, polygonal, pruritic
• violaceous
• flat-tipped papules
• Small, shiny, lichenified plaques
• Symmetrical and flat-tipped
• location
  • usually appears in the genital or anal areas of your body but can affect any other regionss
  • Flexor surfaces: wrists, forearms, groin, ankles
  • Can affect oral mucosa—lacy white streaks (Wickham striae) or papules or ulcers
  • Can affect nails, scalp and genital mucosa – 10% have lichen planus of the nails
• 1 in 100 people worldwide
• adults over the age of 40 years. About half those affected have oral lichen planus, which is more common in women than in men (most common on the vulvas of women)
• Prognosis
  • Cutaneous lichen planus tends to clear within a couple of years in most people,
  • but mucosal lichen planus is more likely to persist for a decade or longer.
  • Spontaneous recovery is unpredictable, and lichen planus may recur at a later date. Scarring is permanent, including balding of the scalp

MANAGEMENT

• Explanation and reassurance
  • Cutaneous lichen planus usually resolves over 6-9 months, leaving discoloured marks without scarring
  • Recurrence rare
  • Asymptomatic lesions require no treatment
• General measures
  • Avoid soaps and shower gels that will exacerbate scaling
  • Use emollients regularly
• Sedating antihistamines 
  • may help troublesome nocturnal itch
• Local treatments for the symptomatic cutaneous or mucosal disease are:
  • Potent topical steroids
  • Topical calcineurin inhibitors, tacrolimus ointment and pimecrolimus cream
  • Topical retinoids
  • Intralesional steroid injections
• Systemic treatment for widespread lichen planus or severe local disease often includes a 1 to 3-month course of oral prednisone, while commencing another agent from the following list:
  • Acitretin
  • Hydroxychloroquine
  • Methotrexate
  • Azathioprine
  • Mycophenolate mofetil
  • Phototherapy