Graham Hughes1 and Shirish Sangle2
(1)
The London Lupus Centre, London Bridge Hospital, London, UK
(2)
Louise Coote Lupus Unit, St Thomas’ Hospital, London, UK
Abstract
Thrombocytopenia is an important manifestation of APS. Depending on definitions (principally the cut-off level of platelet count), thrombocytopenia has been recorded in as many as 40% of patients with APS.
18.1 Platelets
Thrombocytopenia is an important manifestation of APS. Depending on definitions (principally the cut-off level of platelet count), thrombocytopenia has been recorded in as many as 40% of patients with APS.
Figure 18.1
A peripheral blood film showing clumping of platelets in Hughes syndrome
The clinical picture is most commonly one of chronic, mild thrombocytopenia – for example, with platelet counts in the 90,000–120,000 range. Severe, symptomatic thrombocytopenia (e.g., under 30,000) is unusual. Having said this, “idiopathic”, thrombocytopenia – ITP – can be the presenting manifestation (sometimes in childhood), of Hughes Syndrome. Likewise, studies of series of patients with ITP reveal up to 25% with positive aPL tests.
18.2 Other Platelet Manifestations
“Pseudo-thrombocytopenia” is the phenomenon where a borderline or low platelet count on an automated count is found to be higher (or even normal) on a visual count. The phenomenon is due to in vitro platelet clumping and is clinically associated with aPL, again supporting the theory that platelet membrane changes may be one mechanism in APS.
Heparin-induced thrombocytopenia has also been reported in association with aPL. Fortunately, this has not proved a significant clinical problem with low-molecular-weight heparins, the heparin treatment of choice.
18.3 Evans Syndrome
This eponymous syndrome is the clinical association of thrombocytopenia and autoimmune haemolytic anaemia. Previously reported in up to 5% of patients with SLE, it is now recognised as being more associated with aPL, some patients going on to develop more widespread features of APS. Positive Coombs’ tests are seen in some 10% of APS patients.
18.4 Thrombotic Thrombocytopenic Purpura (TTP)
TTP is a syndrome characterised by a widespread thrombic micro-angiopathy, notably affecting the CNS and kidney.
Platelets are consumed in the thrombotic process leading to thrombocytopenia and haemorrhage.
Similar pictures are seen in other thrombotic micro-angiopathies such as the haemolytic uraemic syndrome (HUS) and the HELLP syndrome (haemolysis, elevated liver enzymes, low platelets, seen in pregnancy).
The relationship between aPL and TTP is still being worked out; at present it is apparent that a (small) percentage of patients with TTP are aPL positive.
18.5 Leucopenia
Leucopaenia is common in SLE and Sjögren’s – but not necessarily with aPL. Bone marrow ischaemia and infarction have been described.