What are the three most likely differential diagnoses and their rationale for a 25‑year‑old male with acute right‑sided abdominal/back pain radiating to the testicle, fever, anorexia, nausea, and possible constipation?

Top 3 Differential Diagnoses for 25-Year-Old Male with Right-Sided Abdominal/Back Pain and Testicular Pain

The three most likely diagnoses are: (1) acute appendicitis with atypical presentation, (2) nephrolithiasis (kidney stone), and (3) testicular torsion, with appendicitis being the most probable given the constellation of fever, leukocytosis (implied by fever), right lower quadrant pain, and systemic symptoms.

1. Acute Appendicitis (Most Likely)

This is the leading diagnosis despite the atypical testicular pain presentation. 1

Clinical Reasoning:

• Classic features present: Right-sided abdominal pain for 24 hours, fever (102.4°F), anorexia, nausea, and pain that woke him from sleep are highly consistent with appendicitis 1
• The "classic" presentation (periumbilical pain migrating to RLQ, anorexia, nausea/vomiting, fever) occurs in only ~50% of patients, making atypical presentations common 1
• Testicular pain does NOT exclude appendicitis: Suppurative appendicitis can present with acute scrotal/testicular pain through a patent processus vaginalis or referred pain 2, 3
• Appendicitis is the most common surgical pathology causing RLQ pain and accounts for approximately one-third of all acute abdominal pain presentations 1
• The stabbing, cramping quality with progression from intermittent to constant pain over 24 hours fits the typical temporal pattern 1

Critical Pitfall:

The testicular pain may mislead clinicians toward a purely urologic diagnosis, potentially delaying appendectomy. Multiple case reports document suppurative appendicitis initially misdiagnosed as testicular pathology, resulting in delayed treatment and increased morbidity 2, 3

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2. Nephrolithiasis (Ureteral Stone)

Right-sided back pain radiating to the testicle is the classic presentation of ureteral colic. 1

Clinical Reasoning:

• Renal colic is among the most common causes of RLQ pain after appendicitis 1
• Testicular radiation is pathognomonic: Pain radiating from flank/back to ipsilateral testicle strongly suggests ureteral stone 4
• The intermittent-to-constant pattern and severity (8/10) are consistent with stone passage 4
• Young males are at risk, particularly with high caffeine intake (6-7 Mountain Dews + 3 Red Bulls daily suggests significant fluid/electrolyte imbalance) 4

Key Distinguishing Features:

• Fever is LESS common with uncomplicated nephrolithiasis unless there is concurrent infection (obstructive pyelonephritis) 4
• The presence of fever (102.4°F) makes this diagnosis less likely as the sole etiology unless complicated by infection 1
• Patients with renal colic typically cannot find a comfortable position and are restless, whereas this patient finds relief lying in bed 4

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3. Testicular Torsion

While less likely given the clinical picture, this is a surgical emergency that cannot be missed. 5

Clinical Reasoning:

• Testicular torsion can present as lower abdominal pain WITHOUT initial scrotal pain in up to 10% of cases 5
• The patient is in the peak age range (adolescents and young adults) for testicular torsion 5
• Critical teaching point: Testicular torsion should ALWAYS be included in the differential diagnosis of lower abdominal pain in young males 5

Key Distinguishing Features:

• Fever is UNCOMMON in uncomplicated testicular torsion 3, 5
• The presence of fever (102.4°F), anorexia, and nausea makes isolated testicular torsion unlikely 3
• Torsion typically presents with sudden-onset severe testicular pain, though abdominal pain can predominate initially 5
• The external genitalia should be examined in EVERY young male with acute abdominal pain to avoid missing this diagnosis 5

Critical Pitfall:

In 6 of 9 cases in one series, the scrotum and testicles were NOT examined during initial evaluation, leading to delayed diagnosis and testicular loss. 5 Physical examination of the scrotum is mandatory in this patient.

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Diagnostic Approach

CT abdomen and pelvis with IV contrast is the most appropriate initial imaging study given the fever, leukocytosis (implied), and RLQ pain with unclear etiology. 1

Rationale:

• CT has the highest diagnostic yield for appendicitis (sensitivity 85.7-100%, specificity 94.8-100%) and can simultaneously evaluate for nephrolithiasis, abscess, and other causes 1
• Fever with abdominal pain raises suspicion for intra-abdominal infection or abscess, making definitive imaging essential 1
• CT can identify alternative diagnoses in 14.5% of cases where clinical suspicion is incorrect 1
• Ultrasound has significant limitations: The appendix is not visualized in 27.7-45% of cases, and sensitivity/specificity are substantially lower than CT 1

Additional Essential Step:

Scrotal ultrasound with Doppler should be performed if testicular examination reveals abnormalities (tenderness, swelling, absent cremasteric reflex) to rule out torsion, which requires urgent surgical exploration 3, 5

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Summary Algorithm

1. Immediate physical examination must include scrotal/testicular examination 5
2. If testicular examination is abnormal (tender, swollen, abnormal lie, absent cremasteric reflex): Urgent scrotal ultrasound with Doppler ± immediate urologic consultation 3, 5
3. If testicular examination is normal or equivocal: CT abdomen/pelvis with IV contrast to evaluate for appendicitis, nephrolithiasis, abscess, or other pathology 1
4. High index of suspicion for appendicitis should be maintained even with testicular pain, as suppurative appendicitis can present this way 2, 3