Fever + Thrombocytopenia + Hepatosplenomegaly

Differential Diagnosis

1. Malaria (Most Common in Tropical/Endemic Settings)

• Species: P. falciparum (most dangerous), P. vivax, P. ovale, P. malariae, P. knowlesi
• Fever is typically irregular the first week, may become periodic (48-hour cycle for vivax/ovale; 72-hour for malariae)
• Hallmark paroxysm: chills → high fever → sweating
• Physical exam: splenomegaly, mild hepatomegaly; rash and lymphadenopathy are NOT typical (if present, consider another diagnosis)
• Labs: anemia, thrombocytopenia, elevated liver enzymes, renal dysfunction
• P. vivax especially prone to splenic rupture
• Diagnosis: Peripheral blood smear (thick and thin), rapid antigen detection tests (RDTs) for falciparum HRP-2/PfLDH
• Screen any febrile traveler from endemic area with fever >38.5°C of unclear origin
• Goldman-Cecil Medicine, p. 3395

2. Visceral Leishmaniasis (Kala-Azar)

• Primary target: reticuloendothelial system - spleen, liver, bone marrow, lymph nodes
• Incubation: 1-4 months after sandfly bite
• Features: intermittent fever (39-40°C), massive hepatosplenomegaly, agranulocytosis, anemia, thrombocytopenia
• Progressive course: chills, emaciation, weight loss, weakness, epistaxis, purpura
• Late finding: patchy macular skin darkening ("black fever" - melanin deposits) over forehead, temples, perioral area
• Susceptibility to secondary bacterial infections, oropharyngeal ulcers
• Untreated: death ~2 years from onset
• Diagnosis: Bone marrow/splenic aspirate (Leishman-Donovan bodies), rK39 rapid test, PCR
• Treatment: Liposomal amphotericin B (first-line), miltefosine, antimonials (sodium stibogluconate)
• Andrews' Diseases of the Skin, p. 3777

3. Dengue Fever

• Transmitted by Aedes aegypti (day-biting mosquito)
• Incubation: 4-7 days; sudden-onset high fever, severe myalgias ("breakbone fever"), headache, retro-orbital pain, rash
• Thrombocytopenia is characteristic; hepatomegaly common; splenomegaly less pronounced but occurs
• Severe dengue (formerly dengue hemorrhagic fever): pleural effusions, bleeding diathesis, shock - mortality >10%
• Dengue can cause petechial hemorrhages indistinguishable from meningococcemia
• Can mimic influenza, measles, or rubella; lymphadenopathy usually absent (unlike West Nile fever)
• Diagnosis: NS1 antigen (early), IgM/IgG serology, RT-PCR
• Tintinalli's Emergency Medicine, p. 1123

4. Enteric Fever (Typhoid/Paratyphoid)

• In a study of 60 patients with enteric fever, rose spots, relative bradycardia, splenomegaly, thrombocytopenia, and elevated AST had the strongest predictive value
• Stepladder fever pattern; hepatosplenomegaly in the second week
• Relative bradycardia (Faget sign) is an important clue
• Diagnosis: Blood culture (gold standard), Widal test (poor specificity), bone marrow culture (most sensitive)
• Fitzpatrick's Dermatology, p. 1968

5. Hemophagocytic Lymphohistiocytosis (HLH)

• HLH diagnostic criteria (5 of 8 must be met): fever (≥7 days), splenomegaly, cytopenias (including thrombocytopenia), hypertriglyceridemia or hypofibrinogenemia, histologic evidence of hemophagocytosis, low/absent NK cell activity, elevated ferritin (>500 ng/mL), elevated soluble CD25
• Primary (genetic): PRF1, UNC13D, STX11, STXBP2 mutations - autosomal recessive
• Secondary: triggered by infections (EBV most common), malignancy, autoimmune disease
• Markedly elevated ferritin (often >10,000) is a red flag
• Diagnosis: Bone marrow biopsy showing hemophagocytosis
• Goldman-Cecil Medicine; Dermatology 2-Volume Set

6. Disseminated Histoplasmosis

• Subacute disseminated form: fever, weight loss, malaise, oropharyngeal ulcers, hepatosplenomegaly
• Bone marrow involvement: anemia, leukopenia, thrombocytopenia - closely mimics visceral leishmaniasis
• Endemic to Ohio and Mississippi River valleys, Central/South America
• Diagnosis: Urinary/serum Histoplasma antigen, bone marrow culture/biopsy, fungal blood culture
• Medical Microbiology 9e, p. 876

7. Other Important Causes

Diagnostic Approach

Fever + Thrombocytopenia + Hepatosplenomegaly
            |
     Travel history?
    /              \
 Endemic area    No travel
 (malaria zone)       |
    |             Age, immunostatus
 Malaria smear + RDT   consider HLH, leukemia,
 (treat empirically)   EBV, autoimmune
    |
 Negative smear
    |
 rK39 antigen → kala-azar
 Dengue NS1/serology
 Blood cultures (typhoid/brucella)
 CBC differential, LFTs, serum ferritin
 Bone marrow biopsy if unclear

• Peripheral blood smear - malaria (parasites), acute leukemia (blasts), EBV (atypical lymphocytes)
• Serum ferritin - markedly elevated (>5000) in HLH
• rK39 rapid test / splenic aspirate - kala-azar
• Dengue NS1 antigen - first 5 days of fever
• Blood cultures - typhoid, brucellosis
• Bone marrow biopsy - kala-azar, HLH, histoplasmosis, leukemia
• Weil-Felix / scrub typhus serology - in eschar-positive cases

Mnemonic: "MILD FEVER"

• M - Malaria
• I - Infectious mononucleosis
• L - Leishmaniasis (visceral)
• D - Dengue / Disseminated histoplasmosis
• F - Fever (typhoid/enteric)
• E - EBV / Ehrlichiosis
• V - Viral hemorrhagic fevers
• E - Extra causes (HLH, Castleman, leukemia)
• R - Relapsing fever / Rickettsia (scrub typhus)

Clinical Pearl: In any tropical or endemic setting, treat as malaria until proven otherwise. Perform malaria smears urgently - a negative smear does NOT rule out malaria (repeat x3 at 12-hour intervals if initial suspicion is high). The degree of splenomegaly is helpful: massive splenomegaly favors kala-azar or chronic malaria over acute dengue.