A 22-year-old young adult presents to the clinic with complaints of severe fatigue, sore throat, and swollen lymph nodes for the past 2 weeks. Which assessment finding would be most characteristic of infectious mononucleosis?

Splenomegaly with left upper quadrant tenderness is a hallmark of infectious mononucleosis, occurring in 50-60% of cases. Other options like sandpaper rash, high fever with chills, or productive cough are not typical findings.

Correct Answer: 4. Enlarged spleen with left upper quadrant tenderness

Explanation of the Correct Answer

Infectious mononucleosis (IM), most commonly caused by the Epstein-Barr virus (EBV), is characterized by the classic triad of fever, pharyngitis, and lymphadenopathy [1,3]. However, a pathophysiologically significant and clinically critical manifestation is splenomegaly (enlarged spleen), which occurs due to lymphocytic infiltration and hyperplasia within the splenic pulp. This enlargement stretches the splenic capsule, leading to a palpable spleen and left upper quadrant (LUQ) tenderness. This finding is highly characteristic of IM and is a key assessment focus because of the risk of a life-threatening complication: atraumatic splenic rupture ^[2]. The spleen is most vulnerable during the second and third weeks of illness, which aligns with the patient's 2-week history. The tenderness is a direct clinical correlate of capsular distension and potential subcapsular infarction or hemorrhage ^[4]. Therefore, LUQ pain and tenderness in a patient with a mononucleosis-like syndrome should immediately raise concern for splenic involvement, making this the most characteristic and high-stakes assessment finding among the options.

Analysis of Other Options

Option 1: Presence of a sandpaper-like rash on the trunk and extremities. A sandpaper-like rash is a classic dermatological finding for scarlet fever, which is caused by group A Streptococcus pyogenes producing an erythrogenic toxin. While a maculopapular rash can occur in IM, particularly after the administration of ampicillin or amoxicillin, it is not a primary diagnostic feature and is not described as sandpaper-like. This option points toward a streptococcal infection rather than a primary EBV infection.

Option 2: High fever with alternating chills and profuse sweating. This pattern of fever, known as a hectic or Pel-Ebstein fever pattern, is more classically associated with lymphomas, such as Hodgkin's lymphoma, or with deep-seated bacterial infections like an abscess. Although high-grade episodic fever can occur in IM ^[1], the specific cyclical pattern of alternating chills and drenching sweats is not a typical or most characteristic presentation of uncomplicated IM. It is a red flag for other serious underlying conditions that might be part of a differential diagnosis.

Option 3: Productive cough with thick, purulent sputum. A productive cough with purulent sputum is a hallmark sign of a lower respiratory tract bacterial infection, such as pneumonia or acute bronchitis. IM is a viral illness that primarily affects the lymphoreticular system. While pharyngitis is a core symptom, it is typically exudative and painful, not associated with a deep, productive cough. This option describes a pulmonary infectious process, not a systemic lymphoproliferative one.

Deeper Pathophysiology and Clinical Reasoning

To understand why splenomegaly is such a critical finding, you must connect the underlying pathophysiology to the clinical assessment. EBV has a tropism for B lymphocytes, infecting them and causing a massive proliferation of infected B cells. This triggers a robust cytotoxic T-cell response, leading to the accumulation of these reactive atypical lymphocytes (Downey cells) in lymphoid tissues, including the spleen [1,2]. This infiltration causes the spleen to become engorged, hyperemic, and friable. The splenic capsule is stretched, causing the LUQ tenderness on palpation. This is not just a diagnostic clue; it is a direct warning sign. The enlarged, fragile spleen is at high risk for spontaneous rupture, a surgical emergency that can present with sudden, severe LUQ pain radiating to the left shoulder (Kehr's sign), syncope, and hemorrhagic shock ^[2]. Even minor trauma or vigorous palpation can precipitate rupture. Furthermore, complications like splenic infarction can occur, presenting with focal LUQ pain as seen in a case where a wedge-shaped infarct was confirmed on imaging ^[4]. The finding of splenomegaly with tenderness directly informs critical nursing interventions: strict activity restriction, avoidance of contact sports for at least 3-4 weeks, and vigilant monitoring for signs of hemodynamic instability. A rare but severe complication like gastric volvulus, secondary to massive splenomegaly, further underscores the mechanical and life-threatening consequences of an enlarged spleen ^[3].