Deep vein thrombosis

Editor, – I read with interest Drs Tay and McGrath's article 'Diagnosis of deep vein thrombosis' (Aust Prescr 1998;21:76-9) and the challenge it frequently presents. I note that, in the management of isolated calf vein thrombosis without ongoing risk factors, they advocate withholding anticoagulation and repeat the scan in 5-7 days.

An increasing body of literature is finding that non-propagating isolated calf vein thrombosis is indeed embolising to produce both 'serious' symptomatic pulmonary emboli and 'asymptomatic' pulmonary emboli that later result in pulmonary hypertension.

I refer particularly to a Scandinavian study (specifically designed to asses the source of emboli) which showed >35% of patients had an isolated calf deep vein thrombosis.¹

Other studies found that 40%² to46%³ of emboli originated in the calf. A 1993 study⁴ assessed patients with paradoxical emboli via patent foramen ovale; the source was isolated to calf veins in 15 of 24 patients.

While it may be contentious as to the true incidence of isolated versus propagated calf deep vein thromboses embolising, I think it is being increasingly recognised that isolated calf deep vein thromboses are not as 'benign' as was once thought. If this is true, given the potential for both symptomatic and 'asymptomatic' pulmonary emboli to have a high morbidity, should we be anticoagulating these patients rather than repeating their scan subsequently? I would be interested to hear the authors' opinion on this issue.

Rob Ojala
Emergency Department Registrar
Melbourne, Vic.

Dr J.C. Tay and Dr M. McGrath, authors of the article, comment:

Dr Rob Ojala's correspondence highlights one of the current controversies in the management of deep vein thrombosis. As yet, there is insufficient evidence to be dogmatic about management of the isolated calf vein thrombosis, although we would support Dr A.S. Gallus' recommendation about the treatment of symptomatic calf vein thrombosis (Aust Prescr 1998;21:64-6). The emphasis of our review was to describe the diagnostic test options. The value of colour duplex ultrasonography is to provide a means of ongoing non-invasive surveillance of the deep vein thrombosis. This is of particular relevance if a decision is made not to include anticoagulation in managing an asymptomatic isolated calf vein thrombosis.