Serum anti-mitochondrial antibodies and fatigue in primary biliary cirrhosis

Pathogenesis of primary biliary cirrhosis and its fatigue

Primary biliary cirrhosis (PBC) is an autoimmune cholestatic liver disease characterised by a breakdown of immune tolerance to mitochondrial and nuclear antigens, causing injury to the biliary epithelial cells (BEC) lining the small intrahepatic bile ducts. This leads to bile duct injury and the retention of hydrophobic bile acids which cause further BEC injury leading to a self-sustaining cycle of bile duct injury. Initially the BEC respond to injury via a homeostatic response including through proliferation. Ultimately they become senescent; an active process with accompanying release of inflammatory cytokines ('the senescent secretome') which contributes to the process of interface hepatitis which is a feature of high-risk and treatment-unresponsive disease. This model for pathogenesis of PBC has implications for potential therapy approaches in targeting both the 'upstream' immune injury and 'downstream' BEC response to the immune injury. Fatigue is the commonest reported symptom in PBC and has a negative impact on patients' perceived quality of life, often through social isolation. It is unrelated to the severity of liver disease and appears unresponsive to current therapies, including ursodeoxycholic acid and transplantation. Fatigue in PBC is complex, with numerous associated peripheral and CNS features. Initially, cholestasis causes degenerative CNS change affecting areas of the brain regulating autonomic dysfunction and sleep, and these changes lead directly to some manifestations of fatigue and the associated cognitive impairment. In addition to this, the anti-mitochondrial antibody has direct muscle level metabolic effects leading to over-utilisation of anaerobic metabolism. Autonomic dysfunction contributes to the impact of this metabolic change by limiting the capacity of the muscle to respond through increased proton/lactate efflux from cells and outflow from tissues. The model has a number of implications for potential therapy approaches.

The specificity of fatigue in primary biliary cirrhosis: evaluation of a large clinic practice

Quality of life is an important concern for patients with chronic liver disease. We sought to describe the frequency, severity, and associations of fatigue, in patients with primary biliary cirrhosis (PBC). We performed association testing between PBC-40 multidomain disease-specific quality of life responses and clinical findings. Three hundred twenty-seven patients from a single clinic with PBC (94% female, 92% AMA-positive) were evaluated. The average age was 57 years and average disease duration 7.2 years. Verbally reported fatigue was noted in 48% but present in the overwhelming majority on PBC-40 completion, with 44% having moderate or severe symptoms. Of those not complaining of fatigue clinically, 25% documented moderate or severe fatigue by questionnaire. Age had an inverse relationship with fatigue (P < 0.01), whereas body mass index (BMI) was positively associated (P < 0.01), as was the presence of pruritus (P < 0.001), sicca symptoms (P < 0.001), depression (P < 0.001), fibromyalgia (P < 0.004), and scleroderma (P < 0.05). For those with varices (P < 0.05) or cirrhosis clinically (P < 0.05), higher fatigue scores were noted, although those who initially presented with noncirrhotic disease had higher scores at the time of testing (P < 0.005). Fatigue was associated with greater use of prescription medication (P < 0.01), in particular for antipruritics (cholestyramine: P < 0.001; rifampin: P < 0.001), proton pump inhibitors (P < 0.002), beta-blockers (P < 0.02), and antidepressants (P < 0.001), whereas those taking calcium and vitamin D appeared less fatigued (P < 0.05). In a multivariate model, calcium and vitamin D use, BMI, stage of disease at diagnosis, as well as symptomatic fatigue or pruritus, were significant. Biochemical response to UDCA was not associated with lower fatigue scores.

CONCLUSION

Attempts at defining the biological basis of fatigue in patients with PBC, and improving its treatment, must account for its multifactoral causes.