Psoriasis is a chronic inflammatory disease of the skin characterised by a relapsing and remitting course. It manifests as pink, scaly, raised lesions on the elbows, knees, lower back and scalp along with certain nail changes like pitting, discolouration, subungual hyperkeratosis and onycholysis in about 25-50% of the cases. In 5-10% of patients, the disease can be associated with joint involvement.
It is multifactorial in aetiology, with genetic factors and environmental insults playing their role. A positive family history is present in about one third of the patients; when neither parents are affected the risk is about 7.5%, when one parent is affected it is about 15% and when both parents affected, it is 50%. Psoriasis is not contagious.
The following factors may exacerbate the disease:
- Infections (Streptococcal upper respiratory tract infections)
- Medications (Lithium, Antimalarials, Propranolol and other beta blockers, NSAIDS, Terfenadine and steroid withdrawal)
- Winter season
Age of onset is usually 16-22 years and 57-60 years. The lesions vary from a few to numerous and when numerous, tend to be symmetrically distributed.
At the microscopic level, the skin shows excessive cellular proliferation, poor differentiation and inflammation.
Co-Morbidities: Psoriatic patients have been identified as having higher frequencies of hyperlipidemia, coronoray artery disease and myocardial infarction, hypertension, insulin resistance, diabetes mellitus and homocysteinemia. A hospital based case control study has shown an increased prevalence of metabolic syndrome in psoriatic patients that is independent of psoriasis severity.[See Kimball AB below]. Results of a new study at Reykjavik’s Landspitali, the National University hospital of Iceland suggest that patients — especially women — with psoriasis may be at increased risk for metabolic syndrome. The study involving more than 6,500 people found the prevalence of metabolic syndrome to be higher among patients with psoriasis (40 percent) than among those without (23 percent)[See Love TJ et al below]
Role of Diet: Diet has been suggested to play a role in the aetiology and pathogenesis of psoriasis. Diets with low carbohydrates and rich in vegetables and omega 3 polyunsaturated fatty acids (fish such as meckerel, salmons, sardines) improved psoriatic symptoms in some studies.
Animal studies indicate that fatty acids can modulate pro-inflammatory cytokine production and actions. Omega 6 polyunsaturated fatty acids such as arachidonic acid (from meat, refined vegetable oils) enhance interleukin 1 production and tissue responsiveness to cytokines whereas omega 3 polyunsaturated fatty acids such as eicosa pentanoic acid (EPA) and docosa hexanoic acid (DHA) (from fish such as meckerel, salmons, sardines) have the opposite effect. Arachidonic acid is converted to prostaglandin (PG) E2 and leukotreine (LT) B4 which are proinflammatory whereas EPA and DHA are converted into PGE3 and LT B5 which are anti inflammatory. Overproduction of arachidonic acid derived eicosanoids have been implicated in many inflammatory and autoimmune disorders including psoriasis. A diet rich in vegetables and fish is beneficial because it is associated with reduced arachidonic acid intake. Low calorie diet helps in reducing the oxidative stress and thereby improves psoriasis. Weight reduction in obese also helps in improvement of psoriasis.
Low glycemic food improves psoriasis: Diet, metabolic syndrome and psoriasis – Emerging evidence
- Kimball AB et al. National Psoriasis Foundation clinical consensus on psoriasis comorbidities and recommendations for screening. J Am Acad Dermatol. 2008 Jun;58(6):1031-42. Epub 2008 Mar 4. Full Text
- Love TJ et al. Prevalence of the Metabolic Syndrome in Psoriasis. Arch Dermatol. Published online December 20, 2010. doi:10.1001/archdermatol.2010.370. Abstract | Report
- Cohen AD. Psoriasis and the Metabolic Syndrome. Acta Derm Venereol 2007;87:506–509. Full Text
- Gottlieb AB et al. Psoriasis and the Metabolic Syndrome. Journal of Drugs in Dermatology. June, 2008. Full Text
- Sommer DM et al. Increased prevalence of the metabolic syndrome in patients with moderate to severe psoriasis Arch Derm Res. 2006;298(7):321-328. Abstract
- Gisondi P et al. Prevalence of metabolic syndrome in patients with psoriasis: a hospital-based case–control study
British Journal of Dermatology. July 2007;157(1):68–73. Full text
- Wolters M. Diet and psoriasis: experimental data and clinical evidence. Br J Dermatol. 2005 Oct;153(4):706-14. Full Text
- More Evidence of Psoriasis Link to Metabolic Diseases Report
- Prussick RB, Miele L. Nonalcoholic fatty liver disease in patients with psoriasis: a consequence of systemic inflammatory burden? Br J Dermat. July 2018;179(1):16-29. https://doi.org/10.1111/bjd.16239. Available at https://onlinelibrary.wiley.com/doi/full/10.1111/bjd.16239