How to diagnose phlebitis

Mr Eddie Chaloner explains how to differentiate the vascular condition of phlebitis from a DVT.

Phlebitis: infalmmed vein leads to tender lump surronded by erythema

Superficial thrombophlebitis is a localised inflammation of a superficial vein (usually a varicose vein), which presents as a painful, hard lump on the leg, often associated with surrounding erythema.

The correct diagnosis needs to be made. A more significant pathology, such as DVT or a cellulitic skin infection, which could worsen and become serious, must not be overlooked in these cases.

An accurate diagnosis is crucial, because superficial phlebitis will settle spontaneously over 10-14 days with nothing more than topical anti-inflammatory gel and icepacks, whereas a DVT needs urgent assessment and anticoagulation, and cellulitis requires antibiotics.

The nature of the pathology goes some way towards explaining the diagnostic dilemma.

If we reach back into the dimly remembered past of medical school pathology lectures, the concept of 'Virchow's triad' (initially proposed by the eponymous 19th century German pathologist) is still useful today. Fundamentally, Virchow said that if blood clots inside a blood vessel, it is because there is a problem with the blood itself (that is, a thrombophilia), or with the vessel wall or external compression of the vessel.

Angiogram showing Phlebitis Vessel wall

In the case of phlebitis, the most common reason for the IV clotting is a problem with the vessel wall - that is why it mostly occurs in a varicosed or dilated vein.

The intima of a varicose vein when seen at surgery is frequently roughened and thickened, due to the chronic stretching of the vessel, and it is this roughened surface that acts as the nidus for the initial clot formation.

Once the clotting process starts, the vein itself becomes inflamed, leading to the clinical presentation of a hard, tender lump surrounded by erythema. Over the course of a week or two, the inflammation will spontaneously subside and the clot will disperse.

Exclude other pathologies

Generally speaking, superficial phlebitis will not lead to generalised calf swelling and should not prevent the patient from walking normally. Simple investigations, such as a D-dimer test, are often not helpful, because D-dimer will be elevated in both DVT and superficial phlebitis. The gold standard test is a duplex ultrasound scan to check for patency of the deep veins, but this usually requires the patient to attend the local A&E.

As far as cellulitis goes, the erythema around a phlebitic vein can look alarming and may easily be mistaken for an infected insect bite. However, the patient is usually systemically well and there should be no signs of purulent discharge or abscess formation on the lump.

Cellulitis may show some of these characteristics, plus possibly enlarged groin lymph nodes and a fever. Phlebitis is an inflammation, not an infection, so treating it with antibiotics is not effective.

On rare occasions, a severe superficial phlebitis may denote a problem with intravascular clotting. I remember diagnosing an early pancreatic cancer in a patient presenting with bilateral spontaneous phlebitis caused by a neoplastic coagulopathy, but this is very much the exception rather than the rule.

The diagnosis is made on clinical grounds, which is not always easy unless you have seen many cases before, and particularly not in primary care, with limited access to skilled ultrasound services. As ever, the repeated clinical review is useful in avoiding mistakes.


Superficial phlebitis in a varicose vein will frequently recur, because the resolution of the inflammation does not alter the basic underlying problem with the damaged vein surface. Therefore, for these patients, a referral for definitive treatment may be sensible to prevent recurrence.

  • Mr Chaloner is a consultant vascular surgeon at Lewisham Hospital, London, and at Radiance Health, London.

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