The topic for this blog is management
of liver disease in people with diabetes. The following are factors
and tests your doctor will be looking for:
Abnormal liver function tests
Given the fact that at least 50% of
people with type 2 diabetes have NAFLD, all people with type 2
diabetes should have an ALT and AST test done as part of their
initial evaluation. At least 95% of patients with a confirmed minor
elevation of ALT or AST have chronic liver disease independent of the
degree of elevation. Thus, it is always necessary to obtain a
specific diagnosis. The most likely etiologies of minor elevations
of ALT/AST are NAFLD, hepatitis C, hepatitis B, and alcohol.
Moderate social drinking, i.e., less than 20 g/day, does not cause an
elevation of liver enzymes. The initial workup should include
testing for hepatitis C (anti-HCV or HCV PCR), hepatitis B (HBV
surface antigen), hemochromatosis (iron and iron saturation), and an
abdominal ultrasound. Patients with hepatitis C, hepatitis B, and
increased iron saturation need referral for further workup and
treatment. Ultrasound has a positive predictive value of 96% for
detecting NAFLD in the absence of other liver diseases.
Unfortunately the negative predictive value is only 19%; thus,
patients with a negative ultrasound will also need referral. The
impact of this approach on cost of care and manpower is not known,
and the cost-effectiveness of screening ALT has not been established,
although the American Association for the Study of Liver Disease is
now recommending yearly ALT screening for everyone.
Fatty liver disease
The diagnosis of NAFLD or NASH should be suspected in any patient
with type 2 diabetes, especially if there are abnormal liver function
tests. It should be specifically looked for in all obese patients
with type 2 diabetes. ALT is typically elevated two- to threefold
above ULN but is often normal. Mild elevations of serum alkaline
phosphatase and glutamyl transferase may be present. Serum ferritin
levels are frequently elevated, while iron and iron-binding capacity
are normal. Ultrasound studies may reveal a diffuse increase in
echogenicity, so-called “bright” liver. The sensitivity of
ultrasound in patients with elevated ALT is 89% with a specificity of
93% for detecting steatosis. If the ultrasound reveals fatty liver,
it is appropriate to look for etiologies other than diabetes such as
dyslipidemia. There are shortcomings to this approach. The
sensitivity of ultrasound decreases greatly as hepatic steatosis
decreases to 30% or less. Most patients with NAFLD found
incidentally or by screening ultrasound have a normal ALT. These
observations suggest that the sensitivity of ultrasound overall is
really not very high. In patients with abnormal ALTs and other
diseases ruled out, the positive predictive value of ultrasound is
96% but the negative predictive value only 19%. Magnetic resonance
spectroscopy is capable of quantitative assessment of steatosis, but
is not indicated for routine clinical practice. Thus, the gold
standard for diagnosis of NAFLD remains the liver biopsy. In
addition, the diagnosis of progressive liver disease (i.e., NASH),
the precursor of cirrhosis, can only be made by liver biopsy.
However, certain patients including those with reversed ALT-to-AST
ratio, hypertriglyceridemia, and thrombocytopenia are at high risk
for progressive disease.
Treatment of NAFLD
Most patients do
not need to be treated. Only patients with biopsy-proved NASH or the
risk factors listed above should be treated. Whether or not all
patients need a liver biopsy is controversial in that the sensitivity
of the risk factors for progressive disease is not known. It is also
not known whether treatment, other than bariatric surgery, affects
the ultimate prognosis. The treatment consists of measures to lose
weight as well as pharmacologic intervention. There are no
FDA-approved treatments and, in fact, no FDA guidelines for approving
drugs for NAFLD.
Exercise and weight reduction.
The initial
treatment of NASH consists of weight loss and exercise, which enhance
insulin sensitivity and result in reduction of steatosis. Rapid
weight reduction, however, may increase necrosis, inflammation, and
fibrosis. This paradoxical effect is thought to be due to an
increase in circulating free fatty acids due to increased lipolysis
seen with fasting. The ideal rate of weight loss is not known, but
l.5 kg/week has been recommended. The ideal content of the diet is
not known. Recent studies have demonstrated that bariatric surgery
either improves or completely reverses steatosis in patients with
obesity with or without diabetes.
Pharmacologic therapy.
Pharmacologic
therapy of NAFLD is evolving. While many studies have shown
improvement in steatosis, there are neither long-term studies to
determine whether they alter the natural history of the disease nor
studies to indicate whether relapse occurs after treatment
withdrawal. Gemfibrozil, vitamin E, metformin, betaine,
pioglitazone, rosiglitazone, atorvastatin, losartan, orlistat, and
pentoxifylline have all been tried and have all been shown in small
trials to improve liver enzymes. Modest histologic improvement over
6–12 months is seen with some of the agents. Long-term outcome
trials with the various treatment modalities are yet to be completed.
Given that insulin
resistance is central to the pathogenesis of NAFLD,
insulin-sensitizing agents should have utility (even in the absence
of diabetes), and there is increasing evidence that they do.
Metformin has shown mixed results in human trials with some
improvement in ALT but not in histology. Two long-term trials
initiated by the National Institutes of Health are underway. At this
time, treatment with metformin is not recommended outside of
clinical trials. In the meantime, it seems reasonable to treat
patients with NASH and type 2 diabetes with TZDs, recognizing that
the patients may gain weight. In the absence of a histologic
diagnosis of NASH, only those with risk factors for progressive
disease as mentioned above should be treated. TZDs, despite
shortcomings, are emerging as the treatment of choice even in the
absence of diabetes. Statins may reduce hepatic fat content in
patients with hyperlipidemia and NASH.
In summary, the
ideal therapy for NAFLD is yet to be identified, and no
evidence-based recommendations can be made. Outside of clinical
trials, therapy should be directed toward the underlying etiology.
Hepatitis C.
The most effective
treatment of HCV is a combination of pegylated α-interferon and
ribavirin. Interferon, however, affects insulin sensitivity and
glucose tolerance. Studies in non-diabetic patients report that
interferon impairs glucose tolerance. Given the unpredictable effect
of interferon in diabetes, it is reasonable to monitor diabetes
carefully when using interferon.
SUMMARY—
Type 2 diabetes is
associated with a large number of liver disorders including elevated
liver enzymes, fatty liver disease, cirrhosis, hepatocellular
carcinoma, and acute liver failure. In addition, there is an
unexplained association with HCV. The SMR for cirrhosis is higher
than that for CVD in type 2 diabetes. Many consider NAFLD to be
part of the insulin resistance syndrome. However, the presence of
liver disease (unless decompensated) has little implication for the
specific treatment of diabetes, and the presence of diabetes has
little implication for the specific treatment of liver disease.
Patients with decompensated liver disease are more susceptible to
hypoglycemia and require careful monitoring. There continues to be
a need for long-term placebo-controlled trials for the treatment of
NAFLD and for the treatment of diabetes in patients with liver
disease.