Likely explanation: Post-Dengue (Convalescent) Syndrome

• Arthralgia after dengue is reported, but it usually does NOT progress to true arthritis (joint swelling/destruction), unlike chikungunya, which causes a much more prominent and often chronic inflammatory arthritis - Firestein & Kelley's Textbook of Rheumatology. So persistent joint pain without swelling is consistent with post-dengue arthralgia rather than a new inflammatory arthropathy.
• Age (50) and pre-existing hypertension are risk factors for a slower, more symptomatic recovery. Older patients and those with comorbidities tend to have more pronounced and prolonged post-dengue fatigue, myalgia/arthralgia, and headache than younger, healthier patients.
• Headache and tiredness overlap with generic post-viral asthenia, but you should still actively rule out the differentials below before labeling it purely "post-viral," particularly because she's 50 and hypertensive.

Differentials to actively exclude before settling on post-dengue syndrome

1. Persistent/rebound thrombocytopenia or mild anemia from the dengue illness - causes fatigue, sometimes headache.
2. Dehydration / electrolyte disturbance from the febrile illness, worsened if she's on diuretics or ACE inhibitors for BP.
3. Uncontrolled or rebound hypertension - headache and fatigue in a 50-year-old hypertensive must always prompt a BP check; dengue-related fluid shifts and any temporary medication interruption during the acute illness can destabilize BP control.
4. Reactive/secondary arthritis or an unmasked autoimmune process - dengue infection has been associated in some cohort data with increased flares in patients with underlying rheumatic disease (RA/SLE), and some population-based data suggest a modest association between dengue history and later autoimmune rheumatic disease, though this is not firmly established causally (Frontiers in Medicine, 2021, PMID 34805205).
5. Anemia of any other cause, hypothyroidism, or vitamin D/B12 deficiency - common incidental contributors to fatigue in this age group, unmasked or worsened during convalescence.
6. Rarely, post-dengue neurological complications (Guillain-Barré, ADEM, myelopathy) - these are uncommon but should be considered if headache is severe/persistent, there is any weakness, sensory change, neck stiffness, or altered mental status - seek urgent evaluation if any of these appear.
7. Secondary bacterial infection or another concurrent illness unmasked once the dengue fever resolved.

Tests to do

• CBC with platelet count - confirm platelets have normalized and check for persistent anemia.
• ESR and CRP - to distinguish ongoing inflammation (suggesting arthritis/autoimmune flare) versus a normal post-viral state (usually mild/normal).
• Renal function tests and electrolytes (Na, K, creatinine) - important given hypertension and recent febrile illness with possible fluid shifts.
• Liver function tests - dengue commonly causes transaminitis that can take weeks to normalize.
• Blood pressure measurement and review of antihypertensive regimen - to rule out rebound hypertension as a cause of the headache.
• Fasting blood glucose, TSH - simple, cheap tests to rule out common fatigue mimics in a 50-year-old.
• Vitamin D and B12 if fatigue is prominent and prolonged.
• RA factor/anti-CCP, ANA - only if joint pain is accompanied by swelling, redness, warmth, or has lasted beyond 4-6 weeks, to rule out an emerging inflammatory arthritis or autoimmune flare rather than simple post-viral arthralgia.
• Repeat dengue serology (IgG/IgM) is not usually needed if the acute illness was already confirmed and she has clinically recovered; it doesn't change management at this stage.
• If headache is severe, worsening, or has red flags (neurological deficits, neck stiffness, vomiting, altered sensorium) - urgent neurological evaluation/imaging is warranted to rule out rare post-dengue neurological complications.

Management

• Reassurance: this pattern is common and usually self-limited, resolving over 1 to several weeks.
• Rest and gradual return to activity - avoid overexertion, but encourage light mobilization/physiotherapy for joint stiffness rather than complete inactivity.
• Analgesia: paracetamol/acetaminophen is the safest choice for headache and joint pain. Avoid NSAIDs (ibuprofen, naproxen, aspirin) for at least 1-2 weeks after acute dengue, and confirm platelet counts are fully normal before using them at all, because of residual bleeding risk.
• Hydration and balanced diet, with attention to electrolytes.
• Optimize BP control - recheck her antihypertensive regimen since headache in a hypertensive patient always warrants a BP check; adjust medication if BP is elevated or if it was interrupted during the acute illness.
• Treat any identified deficiency (iron, B12, vitamin D) or thyroid abnormality found on testing.
• Follow-up in 2-4 weeks: if joint pain persists with swelling, or fatigue/headache do not improve or worsen, refer to rheumatology/internal medicine for further work-up (to exclude an emerging inflammatory arthropathy or autoimmune process).
• Safety-netting: advise her to seek urgent care if she develops any neurological symptoms (weakness, numbness, confusion, severe unrelenting headache), chest pain, breathlessness, or signs of bleeding.