Prevalence of metabolic syndrome in patients with psoriasis

Introduction

Psoriasis is a chronic inflammatory skin disease that affects 1-3% of the population. ^[1],[2] Epidemiological research has shown that hypertension, heart failure and diabetes are significantly more common in patients with psoriasis than in controls. ^[3] Moreover, an increased mortality from cardiovascular disease in patients with severe psoriasis has been documented and psoriasis may confer an independent risk of myocardial infarction especially in young patients. ^[4] Major factors that may contribute to this unfavorable cardiovascular risk profile include cigarette smoking, obesity, physical inactivity, hyperhomocysteinemia and psychological stress, which have a higher prevalence among patients with psoriasis. Obesity is associated with severe psoriasis and is reported about twice as frequently among psoriasis patients as in the general population. ^[3],[5] The association between psoriasis and metabolic syndrome is also true for mild severity psoriasis and is independent from the tendency of psoriatic patients to be obese. ^[5]

Methods

This study was conducted within a duration of eighteen months (January 2008 to June 2009), in the Department of Dermatology, STD and Leprosy, SMHS Hospital (associated teaching hospital of Government Medical College Srinagar, Jammu and Kashmir, India). The study was a hospital-based case-control study involving a series of 150 patients. Inclusion criteria for patients were age more than 18 years, disease duration of at least six months and not receiving any systemic treatment for psoriasis for at least one month before enrolment. The controls were patients with insignificant complaints, attendants of patients and staff members of the hospital. The source population for cases and controls was the same. An informed consent was taken from all patients and patient characteristics were recorded on a standard proforma. Statistical analysis of the data was done using statistical processing software (SPSS-17) and epi-info software.

Relevant data included age, gender, weight, height, body mass index, waist circumference, blood pressure, smoking habit, age of onset and duration of psoriasis, type and severity of psoriasis. Body mass index (BMI) was calculated as weight in kilograms/height ² in meters. To determine waist circumference, we located the upper hip bone and placed the measuring tape at the level of the upper most part of the hip bone around the abdomen (ensuing the tape measure was horizontal). The tape measure was snug but did not cause compression on the skin. Blood pressure was recorded as the average of two measurements after subjects have been sitting for five minutes. Severity of psoriasis was assessed according to psoriasis area and severity index (PASI) and percent body surface area (%BSA) involvement. Chronic plaque psoriasis was considered to be localized or disseminated when it covered less or more than 10% of the BSA involvement. Metabolic syndrome was diagnosed by the presence of three or more of the five criteria of the National Cholesterol Education Programme′s Adult Panel III (ATP III): waist circumference > 102 cm in men or > 88 cm in women; hypertriglyceridaemia > 1.7 mmol/l (150mg/dl); high density lipoprotein (HDL) cholesterol < 1.0mmol/l (40mg/dl) in men or < 1.3mmol/dl (50mg/dl) in women; blood pressure > 130/85 mmHg; fasting plasma glucose of > 6.1 mmol/l (100mg/dl). ^[6] Venous samples were taken at the enrolment visit after the subjects had fasted overnight (at least 8 h). Serum cholesterol and triglycerides were measured with enzymatic procedures. Plasma glucose was measured using a glucose oxidase method. The study was approved by the institutional ethical committee.

Results

The study included 150 cases and 150 controls with descriptive chracteristics of each group given in [Table - 1]. Psoriasis area and severity index (PASI) score ranged from 2.3 to 70 (median PASI=13.05). Body surface area (BSA) involved ranged from 2% to 90%, with a median BSA involvement of 20. Ninety seven patients had involved BSA > 10% while fifty three had involved BSA < 10%. Disease duration in cases ranged from six months to thirty years with a mean disease duration of 6.67 years.

Table 1 :Descriptive characteristics of cases and controls

We found a higher prevalence of metabolic syndrome in cases (42/150= 28%) than in controls (09/150 = 6%) with an odds ratio (OR) of 6.09, P < 0.05 after adjusting for confounding by age. Individual components of metabolic syndrome like hypertriglyceredaemia, impaired fasting plasma glucose and hypertension were also more prevalent in cases than in controls. The prevalence of various components of metabolic syndrome in cases and controls along with odds ratio and P value are given in [Table - 2].

Table 2 :The distribution of clinical and laboratory findings in cases and controls

Comparing psoriatic patients with and without metabolic syndrome, we observed that patients with metabolic syndrome had longer mean disease duration than psoriatic patients without metabolic syndrome as in [Table - 3]. There was no difference regarding psoriasis severity, gender or prevalence of smoking.

In all age groups we observed higher prevalence of metabolic syndrome among cases than controls. We also observed an early onset of metabolic syndrome in patients of psoriasis [Figure - 1].

Table 3 :Descriptive features of psoriatic patients with and without metabolic syndrome

Figure 1 :Comparing prevelance of metabolic syndrome among different age groups of cases and controls

Discussion

The hypothesis that the atherosclerotic and the psoriatic plaques are the two offshoots of same root is a focus of current research. The following few recent advances in the understanding of atherosclerosis, psoriasis and metabolic syndrome beget the consideration of exploring a common etiopathogenetic pathway for the diseases.

1. Atherosclerosis represents an ongoing low-grade systemic inflammatory state. ^[7]
2. Psoriasis represents a systemic inflammatory disease. ^[8]
3. Psoriatic patients have higher prevalence of metabolic syndrome. ^[5],[9]
4. Psoriasis confers an independent risk for adverse cardiovascular events. ^[10]

Although the exact etiopathogenetic link is yet to be elucidated, certain proinflammatory cytokines and immunological mediators which are shared by the pathognetic mechanisms of the two diseases have been identified. Proinflammatory cytokines like TNF-a and IL-6, which are over expressed in psoriasis plaques, are known to contribute to features of the metabolic syndrome, such as hypertension, dyslipidaemia and insulin resistance. ^[11] Similar to psoriasis, the metabolic syndrome is characterized by an increase in the immunological activity of type 1 helper T cells (T _H 1). ^[12]

Many studies have been published on psoriasis vis-ΰ-vis metabolic syndrome or individual components of metabolic syndrome. Our study observed a higher prevalence of metabolic syndrome among psoriatic patients than the controls [28% vs 6%, odds ratio (OR) 6.09, P = <0.05] which is similar to the results of a well designed, good volume, cross-sectional study by Gisondi et al.[5] [30.1% vs 20.6%, OR 1.65, P=0.005]. Further more, Sommer et al.[13] also found higher prevalence of metabolic syndrome among hospitalized psoriatic patients as compared to hospitalized melanoma patients but the study instead of ATP III criteria adopts a modified version of the WHO definition of metabolic syndrome. In comparison to studies of Gisondi et al.[5] and Sommer et al.[13] our study has the drawback of being controlled for confounding via adjustment for age only, instead of age and gender. But the effect of such confounding should be little keeping in view of the fact that in a data which is adjusted for confounding by age, the low prevalence of metabolic syndrome in premenopausal women as compared to males is balanced by its relatively higher prevalence in post menopausal women.

In contrast to Gisondi et al.[5] study which documented the higher prevalence of metabolic syndrome in psoriatic patients than controls after the age of 40 years, ^[5] we observed the higher prevalence in psoriatic patients right from the late second decade (12.9% vs 0% in the age group 18 - 30 years), [Figure - 1]. We also observed longer mean disease duration in psoriatic patients with metabolic syndrome than those without metabolic syndrome. It is possible that depression, eating habits, psychosocial inactivity, stress and inflammatory mediators associated with psoriasis favor metabolic syndrome. Such an association also suggests that psoriatic patients without metabolic syndrome need to be counseled properly so that behavioral modification in association with appropriate management of their psoriasis may make the emergence of cardiovascular risk factors less likely.

Association of psoriasis with individual components of metabolic syndrome had been a focus of many cross-sectional studies in the recent past. Results from such studies are varied and inconsistent with regard to dyslipidemia. Several studies with varying population and analytical approaches have found an association between psoriasis and increased prevalence of diagnosis of dyslipidemia. ^{[14],[15],[16]} In addition, multiple studies have documented increased prevalence of diabetes and hypertension in patients with psoriasis. ^{[13],[17],[18]}

Niemann et al.[9] used the General Practice Research Database and found higher rates of diabetes mellitus, hypertension, hyperlipidaemia, obesity and smoking in patients with psoriasis than in controls. ^[9] The same authors also found that patients with severe psoriasis had higher rates of obesity and diabetes mellitus than those with mild psoriasis. Our study also showed a higher prevalence of metabolic syndrome in psoriatic patients. We also observed the higher prevalence of individual components of metabolic syndrome like triglyceride levels >150 mg/dl (73/150 vs 24/150 OR= 4.98, P=0.0005), fasting plasma glucose > 100 mg/dl (27/150 vs 08/150 OR=3.90, p =0.0006) and blood pressure >130/85 (74/150 vs 24/150 OR=5.11, P=0.0005) in patients of psoriasis than in controls, [Table - 1]. Such an association prompts one at looking upon atherosclerotic and psoriatic plaques as related closely to each other but the conclusion awaits establishment of a common or at least closely related etiopathogenetic mechanism. Studies on such an association, till now, point toward the primary role of insulin resistance for both metabolic syndrome and chronic inflammatory state of the body. Therapeutic intervention based on methotrexate and tumor necrosis factor (TNF)-a antagonists seem to diminish the insulin resistance state. An atherogenic lipid profile at the onset of psoriasis has been observed in a well-designed study, which excluded the possible role of confounding factors such as obesity, hypertension, cigarette smoking and physical activity. ^[10]