20 year old complaints of abdominal pain

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Differential Diagnosis: Acute Severe Abdominal Pain in a 20-Year-Old

A 20-year-old with acute severe abdominal pain has a broad differential. At this age, the most common and important diagnoses differ from older adults (e.g., AAA is rare; appendicitis, ectopic pregnancy, and IBD are common). The key is to immediately rule out life-threatening causes before addressing the more common ones.

STEP 1: Red Flags - Must-Not-Miss (Life-Threatening)

These require immediate identification. Any of the following should trigger urgent workup:

Condition	Key Features
Acute appendicitis	Periumbilical pain migrating to RLQ, anorexia, low-grade fever, rebound tenderness at McBurney's point
Ruptured ectopic pregnancy	Female, LMP history critical; sudden pelvic/lower abdominal pain, vaginal bleeding, hemodynamic instability
Perforated peptic ulcer	Sudden-onset epigastric pain, board-like rigidity, free air on X-ray
Acute mesenteric ischemia	"Pain out of proportion to examination," vomiting, bloody diarrhea
Bowel obstruction (strangulated)	Colicky pain, vomiting, no stool/flatus, distension
Ruptured ovarian cyst / adnexal torsion	Female, sudden-onset pelvic pain, nausea/vomiting

Symptom to Diagnosis, 4th Ed.
ROSEN's Emergency Medicine, 9th Ed.

INTRA-ABDOMINAL CAUSES (by region)

Right Upper Quadrant (RUQ)

Biliary colic / acute cholecystitis - crampy RUQ pain radiating to the right subscapular area, post-prandial; usually peaks age 35-60 but can occur in young adults, especially females or those with risk factors
Acute hepatitis - dull RUQ, jaundice, elevated LFTs
Peptic ulcer disease - epigastric, gnawing; worse with food/empty stomach

Epigastric

Acute pancreatitis - epigastric pain radiating to the back, nausea/vomiting, elevated lipase/amylase (in 20-year-olds: consider alcohol, gallstones, trauma)
GERD / esophagitis - burning, postprandial

Right Lower Quadrant (RLQ)

Acute appendicitis - #1 surgical emergency in this age group; periumbilical pain migrating to RLQ over 8-12 hours
Meckel's diverticulitis - clinically indistinguishable from appendicitis
Terminal ileitis / Crohn's disease - chronic/recurrent; RLQ pain, diarrhea, weight loss
Mesenteric lymphadenitis - common in young patients, often post-viral; RLQ pain mimicking appendicitis

Left Lower Quadrant (LLQ)

Diverticulitis - rare at 20 but possible; LLQ pain, fever
Sigmoid volvulus - young patients in endemic areas

Diffuse / Periumbilical

Gastroenteritis - crampy, diffuse, associated diarrhea/vomiting
Bowel obstruction - distension, colicky pain, vomiting, no flatus
Mesenteric ischemia - severe diffuse pain, out of proportion to exam findings
Peritonitis (primary or secondary) - generalized rigidity, guarding, rebound

GYNECOLOGICAL CAUSES (females specifically)

These are extremely common in 20-year-old females and must always be considered:

Condition	Features
Ectopic pregnancy	Always check serum beta-hCG first; sudden pelvic/unilateral pain, hemodynamic instability
Adnexal torsion	Sudden-onset severe unilateral pain, nausea/vomiting, palpable adnexal mass; Doppler shows absent blood flow; surgical emergency
Ruptured ovarian cyst	Acute onset; Lutein cyst rupture can cause significant intra-abdominal hemorrhage
Pelvic Inflammatory Disease (PID)	Lower abdominal pain, cervical motion tenderness, fever, vaginal discharge
Endometriosis	Cyclic or non-cyclic pelvic pain, dysmenorrhea
Tubo-ovarian abscess	Fever, adnexal mass, sexually active

Bailey & Love's Surgery, 28th Ed. (p.2334)
S. Das Manual on Clinical Surgery, 13th Ed. (p.472)

UROLOGICAL CAUSES

Ureteric / renal colic - sudden flank/loin-to-groin pain, colicky, hematuria; restless patient; CVA tenderness
Acute pyelonephritis - fever, loin pain, dysuria

EXTRA-ABDOMINAL CAUSES

These can mimic an acute abdomen and must not be forgotten:

Thoracic

Basal pneumonia / pleurisy - referred abdominal pain, respiratory symptoms
Pulmonary embolism
Myocardial infarction - rare at 20 but possible (congenital anomalies, Kawasaki disease sequelae); epigastric pain

Metabolic / Systemic

Diabetic ketoacidosis (DKA) - severe diffuse abdominal pain, nausea/vomiting; check glucose, ketones
Sickle cell crisis - abdominal pain in sickle cell patients
Acute porphyria - recurrent severe abdominal pain, neuropsychiatric features, dark urine
Addisonian crisis - adrenal insufficiency, hypotension, abdominal pain
Malaria / typhoid fever - in endemic areas or returning travelers

Musculoskeletal

Rectus abdominis hematoma/tear
Herpes zoster (pre-eruptive phase) - dermatomal distribution

CLINICAL APPROACH SUMMARY

Pivotal features to assess immediately:

Peritoneal signs (rebound, rigidity, guarding) - suggests catastrophe (perforation, infarction, hemorrhage)
Hemodynamic instability - rupture, sepsis, hemorrhage
Abdominal distension - obstruction or free air/fluid

First-line investigations in the ED:

Serum beta-hCG (all females of reproductive age - mandatory)
FBC, CRP, LFTs, amylase/lipase, U&E, urine dipstick
Erect CXR (free air = perforation)
Ultrasound abdomen/pelvis (first-line imaging)
CT abdomen/pelvis with contrast if ultrasound inconclusive (gold standard for most causes)

Important clinical note: In a 20-year-old female with acute severe abdominal pain, ectopic pregnancy and adnexal torsion must be excluded urgently before any other workup - both are surgical emergencies where delay causes mortality or permanent loss of fertility. A serum beta-hCG must be drawn immediately.

Sources: S. Das Manual on Clinical Surgery 13th Ed. | Bailey & Love's Surgery 28th Ed. | ROSEN's Emergency Medicine | Symptom to Diagnosis 4th Ed. | Goldman-Cecil Medicine

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