Methotrexate is one of the commonly used conventional systemic treatment for moderate to severe psoriasis as well as psoriatic arthritis. It is also used as co-therapy with TNF-antagonists to improve efficacy and reduce neutralizing drug antibodies formation. Apart from the bone marrow suppression, which can largely be avoided with careful dosing, monitoring and avoidance of certain drug interaction, hepatotoxicity is one of the major side-effects. Short term rises in hepatic transaminases are well recognized with methotrexate, which is largely reversible. However, the insidious development of liver fibrosis and ultimately cirrhosis is of greater clinical concern given this may be irreversible with significant impact. Methotrexate-induced liver fibrosis is still a concern especially in patients who received high cumulative dose and those with comorbid risk factors such as diabetes and obesity. The prevalence of significant fibrosis and cirrhosis were reported to be 4.5 - 33.3% and 0 - 25.6%, respectively, in liver biopsy series of psoriasis patients on methotrexate. The results were so variable owing to the facts that many studies were old with poor reporting and variable histological scoring system making interpretation difficult.

According to the NICE guideline and British Association of Dermatologist's guideline ( 2016), liver biopsy remains the gold standard in the assessment of liver fibrosis, however, it is a relatively invasive procedure, with potential sampling error and inter-observer variability, leading to decreasing use of liver biopsy as routine for monitoring methotrexate hepatotoxicity . Non-invasive methods to assess liver fibrosis are therefore advocated, including serum indices as well as transient elastography.

Transient elastography has been shown to correlate well with liver fibrosis in chronic hepatitis and has been widely adopted as a noninvasive method to assess liver fibrosis in various chronic liver disease, but not yet in this specific Psoriasis patients on methotrexate. There is increasing trend to use transient elastography for detection of methotrexate-associated liver fibrosis. However, only few studies included adequate number of patients with concomitant liver biopsy and transient elastography. Data from a study including a relatively high number of patients with liver biopsy (24 psoriasis patients) reported successful scan rate of 83.3% and high negative predictive value of 88% for significant fibrosis. Alternative, Serum procollagen III level (PIIINP) for liver fibrosis is only available in selected specialist centres oversea but not in HK and is costly. Currently, psoriasis patients on methotrexate with cumulative dose of 3000mg of above are advised to have USG guided Fine-needle aspiration (FNA) liver biopsy to assess the presence of liver fibrosis with severity grading , according to American Academy of Dermatology Guideline in Methotrexate dosing. For patient with liver fibrosis grading of 3 a or above ( Roenigfk classification) , they are advised to stop methotrexate and switch to alternative medication. In view of the demand of a safer and reliable non-invasive test to detect advanced liver fibrosis in psoriasis patients receiving methotrexate, we propose to recruit these patients for a paired transient elastography assessment and liver biopsy.