Differential diagnosis

Although acute appendicitis is the most common abdominal surgical emergency, the diagnosis at times can be extremely difficult. It is important to remember that many conditions which mimic appendicitis also require surgical intervention, or if they do not are rarely made worse by appendicectomy. However, there is a number of common conditions that it is wise to consider carefully and, where possible, exclude. The differential diagnosis differs in patients of different ages and in adult life, females have the added differential of diseases of the female genital tract (Table 59.5).

Children

The diseases most commonly mistaken for acute appendicitis are acute gastroenteritis and mesenteric lymphadenitis. In acute gastroenteritis there is intestinal colic together with diarrhoea and vomiting, but localised tenderness does not usually occur. There is often a history of other family members being affected. Post ileal appendicitis may mimic this condition, thus hospital admission and careful observation are warranted. Where serious doubt persists laparoscopy or surgical exploration may be indicated. In mesenteric lymphadenitis, the pain is colicky in nature and the patient may be completely free from pain between attacks, which last for a few minutes. Cervical lymph nodes may be enlarged. If present, shifting tenderness when the child turns on to his or her left side is convincing evidence. The condition presents a common diagnostic difficulty in children and if doubt exists exploration is advisable.

It may be impossible clinically to distinguish Meckel’s diverticulitis from acute appendicitis. The pain is similar, however signs may be central or left-sided. Occasionally, there is a history of antecedent abdominal pain or anaemia.

It is important to distinguish between acute appendicitis and intussusception. Appendicitis is uncommon before the age of 2 years, whereas the median age for intussusception is 18 months. A mass may be palpable in the right lower quadrant and the preferred treatment of intussusception is reduction by careful barium enema.

Henoch—Schönlein purpura

This is often preceded by a sore throat or respiratory infec­tion. Abdominal pain can be severe and be confused with intussusception or appendicitis. There is nearly always an ecchymotic rash, typically affecting the extensor surfaces of the limbs and on the buttocks. The face is usually spared. The platelet count and bleeding time are within normal limits.

Lobar pneumonia and pleurisy

Lobar pneumonia and pleurisy, especially at the right base, may give rise to right-sided abdominal pain and mimic appendicitis. Abdominal tenderness is minimal, pyrexia is marked and chest examination may reveal a pleural friction rub or altered breath sounds on auscultation. A chest radiograph is diagnostic.

Adults

Terminal ileitis

  In its acute form terminal ileitis may be indistinguishable from acute appendicitis unless a doughy mass of inflamed ileum can be felt. An antecedent history of abdominal cramping, weight loss and diarrhoea suggests regional ileitis rather than appen­dicitis. The ileitis may be nonspecific, due to Crohn’s disease or Yersinia infection. Yersinia enterocolitica causes inflammation of the terminal ileum, appendix and caecum with mesenteric adenopathy. If suspected, serum antibody titres are diagnostic and treatment with intravenous tetracycline antibiotic is appropriate. If Yersinia infection is suspected at operation, a mesenteric lymph node should be excised, divided, and half submitted for microbiological culture (including tuberculosis) and half for histological examination.

Ureteric colic

Ureteric colic does not commonly cause diagnostic difficulty as the character and radiation of pain differ from those of appendicitis. Urinalysis should always be performed and the presence of red cells should prompt a supine abdominal X-ray. Renal ultrasound or an intravenous urogram is diagnostic.

Right-sided acute pyelonephritis

This is accompanied and often preceded by increased frequency of micturition. It may cause difficulty in diagnosis, especially in women. The leading features are tenderness confined to the loin, fever (temperature 390C), and possibly rigors and pyuria.

Perforated peptic ulcer

(Duodenal contents pass along the paracolic gutter to the right iliac fossa.) There is usually a history of dyspepsia and a very sudden onset of pain, which starts in the epigastrium and passes down the right paracolic gutter. In appendicitis the pain starts classically in the umbilical region. Rigidity and tenderness in the right iliac fossa are present in both conditions, but in perforated duodenal ulcer the rigidity is usually greater in the right hypochondrium. Radiography may show gas under the diaphragm. continues unabated until operation. Usually there is a history of a missed menstrual period and urinary pregnancy test may be positive. Severe pain is felt when the cervix is moved on vaginal examination. Signs of intraperitoneal bleeding usual­ly become apparent and the patient should be questioned specifically regarding referred pain in the shoulder. Pelvic ultrasonography should be carried out in all cases where an ectopic pregnancy is a possible diagnosis.

Testicular torsion

Testicular torsion in a teenager or young adult male is easily missed. Pain can be referred to the right iliac fossa, and shyness on the part of patient may lead the unwary to suspect appendicitis unless the scrotum is examined in all cases.

Acute pancreatitis

Acute pancreatitis should be considered in the differential diagnosis of all adults suspected of acute appendicitis and when appropriate excluded by serum or urinary amylase measurement.

Rectus sheath haematoma

This is a relatively rare but easily missed differential diagnosis. It usually presents with acute pain and localised tenderness in the right iliac fossa, often after an episode of strenuous physical exercise. Localised pain without gastrointestinal upset is the rule. Occasionally, in an elderly patient, particularly those on anticoagulant therapy, a rectus sheath haematoma may present with a mass and tenderness in the right iliac fossa following minor trauma (Fig. 59.10).

Adult females

It is in women of child-bearing age that pelvic disease most often mimics acute appendicitis. A careful gynaecological history should be taken in all women with suspected appen­dicitis concentrating on menstrual cycle, vaginal discharge and possible pregnancy. The most common diagnostic mim­ics are salpingitis, mittelschmerz, torsion or haemorrhage of an ovarian cyst and ectopic pregnancy.

Salpingitis

This is the condition which poses greatest diagnostic diffi­culty in young women. Typically, the pain is lower than in appendicitis and is bilateral. A history of vaginal discharge, dysmenorrhoea and burning pain on micturition are all help­ful differential diagnostic points. There may be a history of contact with sexually transmitted disease. When suspected, the opinion of a gynaecologist should be obtained, and high vaginal swab taken for Chlamydia culture. When serious diagnostic uncertainty persists, diagnostic laparoscopy should be undertaken.

Mittelschmerz

Midcycle rupture of a follicular cyst with bleeding produces lower abdominal and pelvic pain, typically midcycle. Sys­temic upset is rare, pregnancy test is negative and symptoms usually subside within hours. Occasionally, diagnostic laparo­scopy is required.

Torsion/haemorrhage of an ovarian cyst

This can prove a difficult differential diagnosis. When suspected, pelvic ultrasound and a gynaecological opinion should be sought. If encountered at operation, ovarian cystectomy should be performed, if necessary, in women of child-bearing years. Documented visualisation of the contralateral ovary is an essential medicolegal precaution.

Ectopic pregnancy

It is unlikely that a ruptured ectopic pregnancy, with its well-defined signs of haemoperitoneum, will be mistaken for acute appendicitis, but the same cannot be said for a right-sided tubal abortion, or still more for a right-sided unruptured tubal pregnancy. In the latter, the signs are very similar to those of acute appendicitis, except that the pain commences on the right side and stays there. The pain is severe and

Elderly

Sigmoid diverticulitis

In some patients with a long sigmoid loop, the colon lies to the right of the midline and it may be impossible to differentiate between diverticulitis and appendicitis. A trial of conservative management with intravenous fluids and antibiotics is often appropriate, with a low threshold for exploratory laparotomy in the face of deterioration or lack of clinical response.

Intestinal obstruction

The diagnosis of intestinal obstruction is usually clear, the subtlety lies in recognising acute appendicitis as the occa­sional cause in the elderly. As with diverticulitis, intravenous fluids, antibiotics and nasogastric decompression should be instigated with early resort to laparotomy.

Carcinoma of the caecum

When obstructed or locally perforated, carcinoma of the caecum may mimic or cause obstructive appendicitis in adults. A history of antecedent discomfort, altered bowel habit or unexplained anaemia should raise suspicion. A mass may be palpable (vide infra) and barium enema or colonoscopy is diagnostic.

Rare differential diagnoses

Preherpetic pain of the right 10th and 11th dorsal nerves is localised over the same area as that of appendicitis. It does not shift and is associated with marked hyperaesthesia. There is no intestinal upset or rigidity. The herpetic eruption may be delayed for 3—8 hours. Tabetic crises are now rare. Severe abdominal pain and vomiting usher in the crisis. Other signs of tabes confirm the diagnosis. Spinal conditions are sometimes associated with acute abdominal pain, especially in children and the elderly. These may include tuberculosis of the spine, metastatic carcinoma, osteoporotic vertebral collapse and multiple myeloma. The pain is due to compression of nerve roots and may be aggravated by movement. There is rigidity of the lumbar spine and intestinal symptoms are absent. The abdominal crises of porphyria and diabetes mellitus need to he remembered. A urinalysis should be tested in every abdominal emergency. In cyclical vomiting of infants or young children there is a history of previous similar attacks, and abdominal rigidity is absent. Acetone is found in the urine but is not diagnostic as it may accompany starvation. Typhlitis or leukaemic ileocaecal syndrome is a rare hut potentially fatal enterocolitis occurring in immunosuppressed patients. Gram-negative or clostridial (especially C. septicum) septicaemia can be rapidly progressive. Treatment is with appropriate antibiotics and haematopoetic factors. Surgical intervention is rarely indicated.