Appendicitis is an acute inflammation of the appendix. The appendix is a small, narrow tube of about 5cm to 10cm, which is connected to the caecum, part of the large intestine, just before the colon.¹ It is not believed to have a specific function in the body. 

Appendicitis is thought to be caused by infection secondary to an obstruction inside of the appendix. The main causes of obstruction are hard masses of faecal matter, normal stools and lymphoid hyperplasia, secondary to viral infection. Other causes include fragments of indigestible food, mucus, parasites and/or tumours. Obstruction results in increased pressure, bacterial overgrowth (most commonly Bacteroides fragilis and Escherichia coli), ischaemia, and necrosis of the appendix, leading to perforation in some people.^1,2

Risk factors for appendicitis include age, male gender, frequent antibiotic use and smoking. Appendicitis is most common between the ages of 10 and 20 years, but can occur at any age, although it is rare before the age of two years. It is slightly more common in men than women, with a male to female ratio of 1.4 to 1.^2,3,4

Use of antibiotics

A balance of microbial gut flora is important for prevention of infection and digestion. Frequent use of antibiotics leads to imbalance of gut flora that may eventually cause a modified response to viral infection, thereby triggering appendicitis.^2,3,4

Smoking

There is an increased incidence of acute appendicitis in smokers compared with non-smokers, and children exposed to passive smoking have a significantly increased incidence of acute appendicitis.^4,5,6

Appendicitis is one of the most common causes of an acute abdomen in adults and children and is the most common non-obstetric surgical emergency in pregnancy, with an incidence of 0.15-2.10 per 1,000 pregnancies.⁵

Complications and prognosis

The most common complication of appendicitis is perforation. This is likely to occur after more than 12 hours of progressive inflammation. The average rate of perforation at presentation is 16-30%; however, this rate is significantly increased in elderly people and young children (up to 97%) and in pregnant women (up to 43%), usually because of a delay in diagnosis. Perforation can lead to abscess, life-threatening infection, sepsis and death. Complications in pregnancy include premature labour or miscarriage and, if there is a delay in diagnosis and treatment, death of both mother and child.^4,6

Appendicitis may resolve spontaneously, but complications are more likely if the appendix is not removed. Appendicectomy, surgical removal of an appendix, is a relatively safe operation. Morbidity and mortality are related to the stage of the disease, and increase after perforation of the appendix. The mortality rate for non-perforated appendicitis is 0.8 per 1,000 people compared with 5.1 per 1,000 people after perforation. Provided there are no complications, recovery from an appendicectomy is usually straightforward. Physical activity may need to be limited for a short period after surgery, three to 14 days depending on the type of procedure used, to aid recovery. ^4,6

Diagnosis

The diagnosis of appendicitis relies on a thorough history and examination. The classic symptoms of appendicitis are abdominal pain (which is the most common presenting complaint in people with acute appendicitis), loss of appetite, nausea, constipation and vomiting. Typically, the person will describe a stomach pain that worsens during the first 24 hours – becoming constant and sharp – and migrates towards the right lower abdomen and pelvic area. The pain is worsened by movement, such as coughing and driving over speed bumps. In children, if asked to ‘hop’ the child will often refuse as this causes pain.^4,5,6

On physical examination, the classic signs of appendicitis are tenderness on percussion, guarding and rebound tenderness. The person may have facial flushing, a dry tongue, halitosis, low-grade fever, not more than 38°C, and/or tachycardia. Be aware that the classic features of appendicitis may not always be present, appearing in only about 50% of people. The symptoms of appendicitis vary and can mimic other conditions that cause abdominal pain.^4,5,6

Presentation can be influenced by the person’s age. In older people, even with advanced inflammation, pain may be minimal and fever absent. The person may also present with confusion and shock. In infants and young children symptoms may include only vague abdominal pain and anorexia, and they may seem withdrawn. 

In pregnancy, pain can be in an atypical area due to displacement of the appendix. Right lower quadrant pain and tenderness dominate in the first trimester. In the latter part of pregnancy, right upper quadrant or right flank pain may occur.⁶

Scoring systems have been developed to aid the diagnosis of appendicitis by estimating the probability of the disease in a person compared with a large number of similar people, using history and examination findings along with inflammatory markers to produce a numerical score. Although there is some evidence that these scoring systems are useful tools in the diagnosis of appendicitis, they are not widely used by clinicians.⁶

Signs of complications include tachycardia and sudden relief of pain, which may be signs of a perforated appendix. An abdominal mass and fluctuating temperature may be signs of an appendix abscess. Profuse vomiting, high fever (more than 40°C), severe abdominal tenderness, and absent bowel sounds may be signs of peritonitis.^4,6

Conditions that may be confused with appendicitis include gastroenteritis, diverticulitis, pyelonephritis, urinary tract infection, ovarian cyst and pelvic inflammatory disease.^1,6

Investigations

There is no single investigation that can completely rule out appendicitis; however, some tests may be useful to support the diagnosis and/or rule out differential diagnoses. 

Simple blood and urine tests may be useful to exclude alternative diagnoses and/or support the diagnosis of appendicitis. A pregnancy test should be taken to exclude pregnancy, including ectopic pregnancy, in women of childbearing potential. 

Urine dipstick test can help exclude a urinary tract infection. Be aware that this may be abnormal in about 50% of people with acute appendicitis because of inflammation adjacent to the right-sided urinary tract and bladder. 

Blood tests including full blood count and C-reactive protein (CRP) can help to rule out infection.^1,4,6

Management 

Appendicitis is a medical emergency that requires immediate hospital assessment and management. Prompt diagnosis and treatment are essential for reducing the risk of complications, which increases with duration of symptoms. Delayed diagnosis and treatment account for much of the mortality and morbidity associated with appendicitis.^1,3,4,6

Immediate hospital admission should be arranged if appendicitis is suspected. There should be a very low threshold for admitting infants and young children, elderly people, pregnant women and people with signs of complications. People at the extremes of ages have increased mortality from appendicitis because of delayed presentation or diagnosis and/or subtle/atypical clinical features.^1,3,4,6

Appendicectomy (surgical removal of the appendix) is the treatment of choice in secondary care for people with appendicitis. This may be done by an open incision in the lower right part of the abdomen (open appendicectomy or laparotomy) or through small incisions in the abdomen with the help of a camera (key hole surgery or laparoscopy). Provided there are no complications, recovery from an appendicectomy is usually straightforward.^1,3,4,6

References 

1. Cox J, Sovak G. Missed appendicitis diagnosis: A case report. Journal of the Canadian Chiropractic Association 2015; 59(3): 294-299
2. Barker D, Morris J. Acute appendicitis, bathrooms, and diet in Britain and Ireland. British Medical Journal 1988; (Clinical Research ed.) 296(6627): 953-955
3. BMJ Best Practice. Appendicitis. BMJ Best Practice 2015; Available from: http://bestpractice.bmj.com/info
4. Jones D. ABC of colorectal diseases. Appendicitis. BMJ 1992; 305(6844): 44-47
5. Andersson R, Lambe M. Incidence of appendicitis during pregnancy. International Journal of Epidemiology 2001; 30(6): 1281-1285
6. Humes D, Simpson J. Acute appendicitis. BMJ 2006; 333(7567): 530-534