Medical Causes of Acute Abdominal Pain
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Direct answer
Medical causes of acute abdominal pain are systemic or extra-abdominal conditions that mimic a surgical abdomen. Diabetic ketoacidosis, acute intermittent porphyria, lead poisoning, sickle cell crisis, lower lobe pneumonia and inferior myocardial infarction are the classic examples. These conditions can cause severe pain with a soft or only mildly tender abdomen, so the diagnosis rests on history, examination and targeted tests. Recognising them avoids an unnecessary laparotomy.
What you must remember
- Diabetic ketoacidosis: hyperglycaemia, ketosis and acidosis, with raised lipase that can mimic pancreatitis.
- Acute intermittent porphyria: abdominal pain with neuropathy, psychiatric features and dark urine.
- Porphyria trigger: drugs such as barbiturates provoke attacks and should be avoided.
- Lead poisoning: colicky pain, constipation, anaemia with basophilic stippling and a lead line on the gums.
- Sickle cell crisis: vaso-occlusive pain that can mimic peritonitis, often with pain at other sites such as bones.
- Lower lobe pneumonia: refers pain to the upper abdomen, so a chest X-ray is part of every acute abdomen.
- Inferior myocardial infarction: epigastric pain with nausea, which needs an ECG with leads II, III and aVF.
Clues that separate the mimics
A young man has severe colicky abdominal pain and constipation, and his abdominal imaging is unremarkable. A clue in his gums and blood film points to lead rather than bowel pathology. Each mimic has a distinctive systemic clue, and the table below pairs each one with the test that confirms it.
| Mimic | Clue | Key test |
|---|---|---|
| Diabetic ketoacidosis | Kussmaul breathing, polyuria, ketones | Blood glucose and blood gas |
| Acute porphyria | Neuropathy, dark urine, drug trigger | Urine porphobilinogen |
| Lead poisoning | Lead line, basophilic stippling | Blood lead level |
| Sickle cell crisis | Known disease, pain at other sites | Sickle screen or electrophoresis |
| Lower lobe pneumonia | Fever, cough, crackles | Chest X-ray |
| Inferior MI | Nausea, sweating, low blood pressure | ECG with leads II, III and aVF |
The abdomen alone often misleads, so the systemic clue should be pursued before any operation. Checking glucose, blood gas, urine, ECG and chest X-ray is quick and avoids surgical error.
Pneumonia and inferior MI are the mimics most easily missed in older adults, because the abdominal examination looks benign and the chest or ECG findings are subtle. A bedside ECG and a chest film should therefore be part of every acute abdomen assessment.
Where the exam tests the surgical mimics
Exam questions reward looking beyond the abdomen to the systemic clue.
- Trap: booking a laparotomy for a soft, minimally tender abdomen Correct: check glucose, blood gas, ECG and chest X-ray first, since mimics are common.
- Trap: attributing epigastric pain with nausea in an older diabetic to gastritis Correct: inferior MI presents this way, so an ECG with leads II, III and aVF is essential.
- Trap: treating a porphyria attack with barbiturates or other enzyme inducers Correct: these drugs trigger attacks, so they are avoided and intravenous haem is given.
Frequently asked questions
What bedside test confirms diabetic ketoacidosis in acute abdominal pain?
Blood glucose and blood gas with ketones establish diabetic ketoacidosis. Raised lipase can occur in diabetic ketoacidosis and may mislead the examiner towards pancreatitis, so the blood gas is the decisive test.
Which urinary test confirms acute intermittent porphyria during an attack?
Urine porphobilinogen is raised during an attack of acute intermittent porphyria and is the key diagnostic test. The attack is typically marked by severe abdominal pain, neuropathy and dark urine, and barbiturates should be avoided.
Why can inferior myocardial infarction present as acute abdominal pain?
Inferior myocardial infarction can cause epigastric pain, nausea and vomiting because the inferior wall of the heart is close to the abdomen and vagal reflexes are involved. An ECG with leads II, III and aVF is needed in any older adult with unexplained epigastric pain.
What clinical features suggest lead poisoning in abdominal colic?
Lead colic produces intense colicky pain, constipation and anaemia, with basophilic stippling on the blood film. A lead line on the gums adds support, and a blood lead level confirms the diagnosis.