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IM6.7-8 | HIV Clinical Evaluation — SDL Guide (Part 3)
Self-Assessment: HIV History and Differential Diagnosis
The following scenario returns to the opening case in a structured format to consolidate your history-taking and differential diagnosis skills. The scenario is designed so that each piece of information you extract from the history narrows the differential. Apply the symptom-CD4 reasoning framework and the structured history sequence you have built before reading the analysis. Consider what additional history items you would prioritise, what examination findings you would look for, and what the top two diagnoses are before investigations.
Scenario — Return to the opening case: A 38-year-old man presents with 10-day progressive confusion, headache, one seizure. His wife found co-trimoxazole in his bag. On initial inspection: oral candidiasis, wasting, bilateral cervical lymphadenopathy. No prior HIV workup available. Before ordering a single investigation, what is your structured history and what are your top two differential diagnoses?
Applying the framework:
History clues and their significance:
- Co-trimoxazole tablets: suggests someone — likely a prior clinician — suspected HIV or documented an OI at CD4 <250 (NACO co-trimoxazole threshold); implies prior HIV exposure to healthcare system.
- Oral candidiasis + wasting: WHO Stage 3; CD4 likely <200.
- Bilateral cervical lymphadenopathy: persistent generalised lymphadenopathy (PGL) is WHO Stage 1, but bilateral cervical LN in this context could be TB lymphadenopathy (firm, matted, ± fluctuant) or reactive lymphadenopathy.
- Progressive confusion + headache + seizure over 10 days: subacute neurological deterioration — the subacute onset over 10 days (not acute as in bacterial meningitis) with an estimated CD4 <200 puts cerebral toxoplasmosis and cryptococcal meningitis at the top of the differential.
Additional history to elicit urgently: HIV diagnosis and ART status; prior TB history; specific neurological history — is the confusion fluctuating or progressive? Any focal weakness, visual changes, or speech changes (focal = toxoplasmosis; global with raised ICP signs = cryptococcus); ART adherence if on treatment.
Examination priorities: Fundoscopy (papilloedema = raised ICP, cryptococcus; CMV retinitis); focal neurological signs; meningism (may be minimal in cryptococcal meningitis); lymph node character (firm-matted = TB); skin for KS.
Top differential diagnosis:
1. Cerebral toxoplasmosis (most common focal CNS lesion at CD4 <100 in India — single or multiple ring-enhancing lesions in basal ganglia, seizures, focal deficit)
2. Cryptococcal meningitis (subacute meningitis, raised ICP, seizures possible, CD4 <100)
3. Differential also includes TB meningitis, HIV encephalopathy, primary CNS lymphoma
Immediate next steps: Urgent CT head (to exclude mass lesion before LP); LP if CT safe; blood CrAg; HIV Ag/Ab test; CD4 count.
CLINICAL PEARL
Two pearls that transform the HIV history from data collection to clinical reasoning. First: the co-trimoxazole clue — finding a co-trimoxazole strip (or Septrin, or TMP-SMX) in a patient's medication list who has not been formally HIV-diagnosed is a clinical red flag; NACO prescribes co-trimoxazole prophylaxis only to PLHIV with CD4 <250, so its presence implies prior clinical suspicion of HIV with likely CD4 below that threshold. Second: the paradox of minimal meningism in cryptococcal meningitis — the inflammatory response that causes the classic neck stiffness of bacterial meningitis requires functional neutrophils and CD4 cells; at CD4 <50, both are severely depleted, so cryptococcal meningitis can present with headache and confusion but near-normal meningism. Never rule out meningitis in HIV on the basis of a flexible neck alone.