Aetiology of psoriasis

The aetiology of psoriasis is multifactorial:

• genetic: (1)
  • about 30% of patients having one first degree relative with psoriasis themselves develop the disease; for patients having two infected first degree relatives, the figure is about 60%
  • there are strong HLA associations (HLA CW6)
    • note - environmental factors are important - monozygotic twin studies show a concordance rate of only 40 to 65%
      
      
• infection: (2)
  • Streptococcal pharyngitis - may cause guttate psoriasis, usually in children and young adults, and within 10-14 days; this pattern is associated with HLA-Cw6 in about 75% of cases
  • AIDS/HIV (3)
  • skin lesions identical to psoriasis may arise in patients with Reiter's syndrome
    
    
• stress, e.g. moving house; examinations
  
  
• trauma:
  • Koebner phenomenon - skin disease occurring in scars or sites of trauma - well recognised in psoriasis
    
    
• drugs:
  • alcohol
  • beta blockers
  • non-steroidal anti-inflammatory drugs
  • antimalarials, e.g. chloroquine
  • mepacrine
  • lithium
  • imiquimod (4)
    
    
• Some treatment methods of psoriasis (e.g., anthralin and phototherapy) - if treated with high initial doses (2)
  
  
• Smoking (5). Alcohol is often cited as a potential risk factor but the evidence for this is not definitive (5)

Reference:

1. Dand N, Mahil SK, Capon F, et al. Psoriasis and genetics. Acta Derm Venereol. 2020 Jan 30;100(3):adv00030.
2. Schon MP, Boehncke WH. Psoriasis. N Engl J Med. 2005 May 5;352(18):1899-912.
3. Morar N, Willis-Owen SA, Maurer T, et al; HIV-associated psoriasis: pathogenesis, clinical features, and management. Lancet Infect Dis. 2010 Jul;10(7):470-8
4. Patel U, Mark NM, Machler BC, et al; Imiquimod 5% cream induced psoriasis: a case report, summary of the literature and mechanism. Br J Dermatol. 2011 Mar;164(3):670-2
5. 2. Wei J et al. Alcohol consumption and smoking in relation to psoriasis: a Mendelian randomization study. Br J Dermatol. 2022 Nov;187(5):684-691