Abdominal Pain in Adults: The Often-Missed Diagnoses

Dr Neeraj Manikath , claude.ai

Abstract

Abdominal pain remains one of the most common presenting complaints in adult medicine, yet certain diagnoses are frequently overlooked or delayed, leading to significant morbidity and mortality. This review examines the oft-missed etiologies of abdominal pain in adults, highlighting diagnostic pitfalls, clinical pearls, and practical approaches to avoid common errors. Understanding these atypical presentations and rare conditions is crucial for postgraduate physicians to improve diagnostic accuracy and patient outcomes.

Introduction

Abdominal pain accounts for approximately 5-10% of emergency department visits and represents a diagnostic challenge spanning multiple organ systems. While common diagnoses such as appendicitis, cholecystitis, and peptic ulcer disease are readily identified, several important conditions are frequently missed or delayed in diagnosis. These missed diagnoses can be categorized into vascular emergencies, extra-abdominal causes, atypical presentations of common diseases, and rare but important conditions.

The consequences of diagnostic delay range from prolonged patient suffering to catastrophic outcomes including bowel infarction, sepsis, and death. This review focuses on building a systematic approach to identify these challenging diagnoses.

Vascular Emergencies

Mesenteric Ischemia

Acute mesenteric ischemia (AMI) carries a mortality rate of 60-80% when diagnosis is delayed, yet it accounts for only 0.1% of hospital admissions, making it a classic "can't miss" diagnosis that is often missed.

Clinical Pearl: The hallmark of mesenteric ischemia is "pain out of proportion to physical examination findings." Patients often writhe in severe pain while the abdomen remains soft with minimal tenderness—a disconnect that should immediately raise suspicion.

Diagnostic Hack: In patients over 60 with sudden-onset severe abdominal pain and atrial fibrillation, cardiac disease, or atherosclerotic risk factors, consider AMI until proven otherwise. Early CT angiography is the diagnostic modality of choice, with sensitivity exceeding 90%. Serum lactate elevation and metabolic acidosis are late findings suggesting bowel infarction.

Oyster: Non-occlusive mesenteric ischemia (NOMI) represents 20-30% of AMI cases and occurs in critically ill patients with low-flow states. It lacks the typical embolic or thrombotic etiology and is particularly easy to miss in ICU patients with multiple competing diagnoses.

Abdominal Aortic Aneurysm (AAA)

Ruptured AAA presents with the classic triad of abdominal/back pain, hypotension, and palpable pulsatile mass in only 25-50% of cases. Atypical presentations include isolated back pain, flank pain mimicking renal colic, or syncope.

Diagnostic Hack: Any patient over 50 with new-onset back or abdominal pain should trigger consideration of AAA, especially in men with smoking history or known vascular disease. Bedside ultrasound can rapidly identify AAA diameter >3 cm, though it cannot reliably detect rupture. CT angiography is definitive.

Pearl: Contained ruptures may present with stable vital signs and gradual symptom progression, creating false reassurance. The presence of abdominal pain with any AAA >5 cm should be considered a surgical emergency.

Abdominal Wall Pathology

Abdominal Wall Hematomas

Rectus sheath hematomas and other abdominal wall bleeding are increasingly common with widespread anticoagulation use but remain underdiagnosed.

Clinical Pearl: Carnett's sign—increased abdominal tenderness when the patient tenses the abdominal wall (lifting head or legs)—suggests abdominal wall rather than intra-abdominal pathology. Intra-abdominal pain typically decreases with wall tensing as the abdominal contents are protected.

Diagnostic Hack: Consider abdominal wall hematoma in any anticoagulated patient with focal abdominal pain, particularly if accompanied by falling hemoglobin without clear source. CT with contrast is diagnostic and reveals the classic spindle-shaped or oval fluid collection within the abdominal wall musculature.

Hernias with Incarceration

Internal hernias, particularly after bariatric surgery, and unusual hernias (Spigelian, obturator, lumbar) are frequently missed because they lack classic findings or external bulges.

Pearl: Post-bariatric surgery patients with intermittent cramping pain and nausea warrant high suspicion for internal hernia, even with normal imaging. Internal hernias may be intermittent and position-dependent.

Oyster: Obturator hernias present with medial thigh pain (Howship-Romberg sign) and occur predominantly in elderly, thin women. This rare hernia has the highest incarceration rate of all hernias.

Hepatobiliary and Pancreatic Causes

Acute Hepatic Porphyria

This autosomal dominant disorder affects heme synthesis and presents with severe abdominal pain, often triggering extensive negative workups before diagnosis.

Clinical Triad: Abdominal pain, neuropsychiatric symptoms, and dark urine (which may only appear after standing or with acidification).

Diagnostic Hack: Consider porphyria in patients with recurrent unexplained abdominal pain, particularly young women, especially when accompanied by hyponatremia, peripheral neuropathy, or seizures. The pain typically lacks peritoneal signs. First-line testing includes spot urine porphobilinogen (PBG), which is markedly elevated during acute attacks.

Pearl: Multiple medications and physiologic stressors trigger attacks. Common culprits include certain antibiotics, barbiturates, alcohol, and hormonal changes.

Sphincter of Oddi Dysfunction (SOD)

Post-cholecystectomy pain syndrome affects 10-20% of patients but is often dismissed as functional.

Diagnostic Approach: Type I SOD presents with typical biliary pain plus abnormal liver enzymes and dilated bile duct—these patients benefit from sphincterotomy. Types II and III are more controversial and challenging to diagnose, requiring hepatobiliary scintigraphy or manometry in specialized centers.

Hack: Before attributing post-cholecystectomy pain to SOD, exclude retained common bile duct stones with MRCP and consider other causes including chronic pancreatitis and functional disorders.

Extra-Abdominal Masqueraders

Myocardial Infarction

Inferior wall MI commonly presents as epigastric pain with nausea and vomiting, mimicking gastroenteritis or peptic disease.

Pearl: Always obtain an ECG in patients over 40 with new epigastric pain, particularly with vascular risk factors. The presence of diaphoresis, dyspnea, or radiation to arm/jaw should heighten suspicion, but these features may be absent in up to 30% of cases.

Hack: Reciprocal changes in inferior leads (ST elevation in II, III, aVF with reciprocal depression in aVL) confirm acute inferior MI even when epigastric symptoms dominate the clinical picture.

Diabetic Ketoacidosis (DKA)

Abdominal pain occurs in 40-75% of DKA cases and may precede or dominate metabolic symptoms. The pain is thought to result from gastric distention, ileus, hepatic capsular stretch, and metabolic acidosis.

Pearl: The severity of abdominal pain in DKA correlates with the degree of acidosis and typically resolves with treatment. However, DKA can also be triggered by intra-abdominal pathology (appendicitis, cholecystitis), creating diagnostic confusion.

Diagnostic Approach: In DKA patients with focal abdominal findings, persistent pain after metabolic correction, or leukocytosis exceeding that expected from stress response (>15,000-20,000/μL), investigate for surgical pathology with appropriate imaging.

Spinal Pathology

Thoracic disc herniation, compression fractures, and radiculopathy can present as abdominal pain following dermatomal distributions.

Pearl: Radicular abdominal pain is typically unilateral, band-like, follows dermatomal patterns (T7-T12), and may be associated with dysesthesias or sensory changes in the distribution. Pain worsens with spinal movement or Valsalva.

Hack: When abdominal examination and initial workup are unrevealing, perform a thorough back examination including palpation of spinous processes and assessment for focal tenderness.

Gynecologic and Urologic Causes

Ovarian Torsion

While typically considered in young women with acute pain, ovarian torsion is missed in postmenopausal women, during pregnancy, and when presentations are subacute.

Pearl: Intermittent torsion-detorsion causes episodic pain that can persist for days to weeks before complete torsion occurs. The presence of ovarian blood flow on Doppler ultrasound does not exclude torsion, as dual blood supply may maintain some perfusion.

Diagnostic Hack: Any woman with acute onset, severe unilateral lower quadrant pain should undergo urgent pelvic ultrasound. Look for enlarged ovary (>4 cm), free fluid, and the "whirlpool sign" of twisted vascular pedicle.

Testicular Torsion with Referred Pain

Men with testicular torsion may present with isolated abdominal or flank pain without testicular complaints, particularly in adolescents.

Pearl: Always examine the testicles in men with abdominal or flank pain. The cremasteric reflex is typically absent in torsion.

Rare but Important Diagnoses

Lead Toxicity

Chronic lead exposure causes severe intermittent cramping abdominal pain, constipation, and anemia. Occupational exposure (battery manufacturing, home renovation with old paint) or use of contaminated traditional medicines creates risk.

Clinical Triad: Abdominal pain, anemia with basophilic stippling, and peripheral motor neuropathy (wrist drop).

Diagnostic Hack: Blood lead levels >40-60 μg/dL typically cause symptoms. Abdominal radiographs may reveal radiopaque foreign material if recent acute ingestion occurred.

Familial Mediterranean Fever (FMF)

This autoinflammatory condition predominantly affects populations of Mediterranean ancestry and presents with recurrent episodes of fever, peritonitis, and serositis lasting 12-72 hours.

Pearl: Patients develop severe peritonitis mimicking acute surgical abdomen, but symptoms spontaneously resolve. Between attacks, patients are completely asymptomatic. The pattern of recurrent self-limited episodes is the key diagnostic clue.

Diagnosis: Genetic testing for MEFV mutations confirms diagnosis. Colchicine is dramatically effective prophylactically.

Abdominal Cutaneous Nerve Entrapment Syndrome (ACNES)

This underrecognized cause of chronic abdominal wall pain results from entrapment of intercostal nerves (T7-T12) as they pierce the rectus abdominis.

Clinical Pearl: Carnett's sign is positive in >90% of cases. The pain is precisely localized to a small (<2.5 cm²) trigger point, typically at the lateral border of the rectus muscle.

Diagnostic and Therapeutic Hack: Injection of local anesthetic at the trigger point provides both diagnostic confirmation (immediate pain relief) and therapeutic benefit. Many patients achieve long-term relief after one to three injections.

Metabolic and Endocrine Causes

Addisonian Crisis

Acute adrenal insufficiency presents with abdominal pain, nausea, vomiting, and hypotension—features that overlap with many intra-abdominal emergencies.

Diagnostic Triad: Hypotension, hyponatremia, and hyperkalemia in a patient with abdominal pain should trigger immediate consideration.

Pearl: Risk factors include chronic steroid use (suppression of HPA axis), bilateral adrenal hemorrhage (in anticoagulated patients), or pituitary apoplexy. The diagnosis cannot wait for confirmatory testing—empiric treatment with stress-dose steroids is appropriate when clinical suspicion is high.

Hypercalcemia

Severe hypercalcemia (>14 mg/dL) causes constipation, abdominal pain, and mental status changes ("stones, bones, groans, and psychiatric overtones").

Hack: Check calcium levels in patients with unexplained abdominal pain, particularly if accompanied by altered mentation, renal stones, or bone pain. Primary hyperparathyroidism and malignancy account for 90% of cases.

Infectious and Inflammatory

Tuberculous Peritonitis

TB peritonitis remains prevalent in endemic areas and immunocompromised patients but is frequently delayed in diagnosis due to insidious onset and nonspecific features.

Clinical Presentation: Chronic abdominal pain, fever, weight loss, and ascites developing over weeks to months. Night sweats occur in approximately 60% of cases.

Diagnostic Approach: Ascitic fluid shows elevated protein (>2.5 g/dL), lymphocytic predominance, and high serum-ascites albumin gradient <1.1 g/dL. Adenosine deaminase (ADA) levels >40 U/L in ascitic fluid have excellent sensitivity and specificity. Peritoneal biopsy with culture and histology provides definitive diagnosis.

Spontaneous Bacterial Peritonitis (SBP)

SBP occurs in cirrhotic patients with ascites but can present with minimal symptoms or be masked by baseline abdominal discomfort from ascites.

Pearl: Maintain high suspicion in any cirrhotic patient with ascites who deteriorates clinically, even without classic peritoneal signs. Fever may be absent in 30-50% of cases.

Diagnostic Hack: Diagnostic paracentesis should be performed liberally in hospitalized cirrhotic patients. SBP is diagnosed with ascitic fluid neutrophil count >250 cells/mm³, even with negative cultures.

Systematic Approach to Avoiding Missed Diagnoses

1. Expand the differential beyond the abdomen: Remember that abdominal pain can arise from cardiac, pulmonary, spinal, metabolic, and hematologic pathology.

2. Age-specific considerations: Vascular emergencies increase dramatically after age 60; young women warrant gynecologic evaluation; consider medication-related causes in the elderly.

3. Red flags demanding urgent investigation:

Pain out of proportion to examination
Hemodynamic instability
Age >50 with new-onset pain
Immunocompromised state
Recent abdominal surgery
Known vascular disease or arrhythmias

4. Strategic use of imaging: CT with IV contrast is highly sensitive for most surgical emergencies but may miss early ischemia, abdominal wall pathology, and functional disorders. Ultrasound excels for biliary, gynecologic, and some vascular pathology.

5. Serial examination: When diagnosis is uncertain, serial examinations over 4-8 hours often clarify the clinical picture and are safer than premature discharge.

6. Think metabolic: Basic laboratories (CBC, comprehensive metabolic panel, lipase, lactate, urinalysis) identify many medical mimics of surgical abdomen.

Conclusion

Missed diagnoses in abdominal pain often result from cognitive biases, atypical presentations, and failure to consider extra-abdominal causes. Anchoring on initial impressions, premature closure, and failure to appreciate the limitations of physical examination all contribute to diagnostic error. By maintaining broad differential diagnoses, recognizing key clinical patterns, and employing strategic diagnostic testing, clinicians can significantly reduce missed diagnoses and improve outcomes for patients presenting with abdominal pain.

The diagnoses reviewed here—from mesenteric ischemia to abdominal cutaneous nerve entrapment syndrome—represent conditions where early recognition dramatically impacts patient outcomes. Familiarity with these clinical presentations, coupled with systematic evaluation approaches, forms the foundation of excellence in managing abdominal pain.

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