Correct Answer: D. Mostly bilateral
DVT is predominantly unilateral, not bilateral. The vast majority of DVT cases (>90%) present with thrombosis confined to a single lower limb, typically the left leg due to anatomical compression of the left iliac vein by the right iliac artery (May-Thurner syndrome). Bilateral DVT is rare and occurs in <10% of cases, usually in specific settings: massive thrombotic burden, malignancy with hypercoagulability, or severe sepsis. In Indian clinical practice, unilateral lower-limb DVT is the standard presentation encountered in post-operative patients, immobilized patients, and those with malignancy. The claim that DVT is "mostly bilateral" fundamentally misrepresents the epidemiology and is therefore the false statement. This distinction is critical because bilateral DVT carries higher morbidity and mortality, requiring more aggressive anticoagulation and consideration of IVC filter placement—making it a clinical red flag rather than the typical presentation.
Why the other options are wrong
A. Some cases may directly present as pulmonary thromboembolism — This is TRUE. Approximately 10–30% of DVT patients present with PE as the first manifestation without prior symptomatic leg swelling, a phenomenon called silent DVT. The thrombus propagates and embolizes before causing local calf symptoms. This is a well-established clinical reality in Indian hospitals where DVT screening is often delayed, allowing time for embolization. This statement is factually correct and cannot be the false answer. B. Most common clinical presentation is pain and tenderness in calf — This is TRUE. Calf pain, swelling, and tenderness are the classic presenting symptoms in symptomatic DVT, occurring in 50–80% of cases. Unilateral calf swelling with positive Homan's sign or pitting edema is the textbook presentation taught in Indian medical schools. While clinical examination is unreliable for diagnosis (requiring imaging confirmation), the symptom itself is the most frequent initial complaint. This statement is factually accurate. C. Clinical assessment is unreliable — This is TRUE. Clinical examination alone has sensitivity and specificity of only 50–60% for DVT diagnosis. Many conditions mimic DVT (cellulitis, Baker's cyst, muscle strain), and up to 50% of clinically suspected DVT is ruled out on imaging. Indian guidelines recommend compression ultrasonography or D-dimer for confirmation rather than relying on bedside signs. This statement correctly reflects the diagnostic uncertainty of clinical assessment and is therefore true.
High-Yield Facts
- Unilateral DVT accounts for >90% of cases; bilateral DVT is rare (<10%) and indicates severe thrombotic disease or malignancy.
- May-Thurner syndrome (left iliac vein compression by right iliac artery) explains the higher incidence of left-sided DVT.
- Silent DVT occurs in 10–30% of cases where PE is the first presentation without prior leg symptoms.
- Calf pain and swelling are the most common symptoms, but clinical assessment alone is unreliable (sensitivity 50–60%).
- Compression ultrasonography is the gold standard for DVT diagnosis in Indian clinical practice; D-dimer is used for risk stratification.
- Bilateral DVT warrants aggressive anticoagulation and consideration of IVC filter due to high PE risk and mortality.
Mnemonics
DVT Laterality Rule Unilateral is Usual (>90%); Bilateral is Bad (rare, ominous sign). Left > Right due to May-Thurner compression. DVT Presentation Triad Calf pain, Swelling, Tenderness = CST. But remember: Clinical assessment is unreliable—always image with ultrasound.
NBE Trap
NBE pairs the word "bilateral" with DVT to exploit students who confuse DVT epidemiology with bilateral leg edema seen in IVC obstruction or heart failure. The trap is assuming symmetrical disease = bilateral DVT, when in reality unilateral DVT is the norm and bilateral presentation is a red flag for malignancy or massive thrombotic burden.
Clinical Pearl
In Indian post-operative wards, unilateral calf swelling in a bedridden patient is DVT until proven otherwise—but never diagnose on clinical grounds alone. Bilateral leg edema in the same patient more likely reflects IVC obstruction or cardiac failure, not bilateral DVT. This distinction changes management dramatically: unilateral DVT gets anticoagulation; bilateral DVT may need IVC filter consideration.
_Reference: Bailey & Love Ch. 32 (Venous Thromboembolism); Harrison Ch. 296 (Venous Thromboembolism)_