Enlargement
of the spleen
The spleen is a meeting place of medicine and
surgery. Table 53.1 summarises the many causes of enlargement of the organ.
Idiopathic
thrombocytopenic purpura
Purpura
Not all cases of purpura (purpura =
porphyra (Greek)
= purple)
benefit from splenectomy. Purpura is defined as local haemorrhage into the skin.
A history of purpura and evidence of it on examination should be sought before
any surgical procedure is undertaken. Purpura may result from the following.
1.
Increased capillary fragility, as in steroid-induced or Henoch—Schönlein
purpura.
2.
Defective platelets (thrombocytopathies), for example, after taking
aspirin which inhibits thromboxane and prostaglandin, and reduces their
property of making the platelet adhesive.
3.
A reduced number of normal platelets (thrombocytopenia). This can be a
consequence of:
(a) decreased platelet
production by marrow megakaryocytes; for example, because of marrow
suppression by cytotoxic chemotherapy or in aplastic anaemia;
(b) increased platelet
consumption, as seen in disseminated intravascular coagulation where the
clotting cascade is triggered by septicaemia and platelets adhere to vascular
endothelium, or in a large haemangioma in which platelets adhere to the abnormal
endothelium;
(c) increased platelet
destruction by the spleen. This may be associated with autoimmune disease (e.g.
systemic lupus erythematosus); with drug reactions, for example, to quinine; and
with certain infections (e.g. mononucleosis). Alternatively, as in ITP, the
platelet destruction may not be associated with any other condition;
(d) increased splenic
sequestration of platelets. This can be associated with any condition that
produces gross splenic enlargement, e.g. portal hypertension.
Splenectomy
may sometimes be helpful in purpura associated with splenic destruction or
sequestration (points 3c and 3d, above). It is most reliably of use in the
management of ITP
Aetiology of idiopathic thrombocytopenic purpura
In most cases the low platelet count in ITP is
due to the development of antibodies which damage the patient’s own platelets
(the normal blood platelet count is 250 x 109—400 x 109/litre).
Transfused platelets have a short survival time after transfusion into patients
with ITP, and the children born to mothers with ITP may have temporary maternal
antibody-induced thrombocytopenia after birth.
Clinical
features
Purpuric patches (ecchymoses) occur in the skin
and mucous membranes which tend to be more prominent in dependent areas because
of a higher, gravity aided, intravascular pressure. A tendency to spontaneous
bleeding from mucous membranes (e.g. epistaxis), and in women to menorrhagia,
and prolonged bleeding of minor wounds is common. Urinary and gastrointestinal
haemorrhage and haemarthrosis are rare. Intracranial haemorrhage is also rare,
but is the most frequent cause of death. Cutaneous ecchymoses may be found on
examination and the tourniquet test is positive. The spleen is palpable in only
25 per cent of cases, and gross splenic enlargement suggests that the diagnosis
is not ITP
Investigations
The bleeding time is increased, but the
clotting and prothrombin times are normal. The platelet count in the peripheral
blood film is reduced (usually less than 60 x 109/litre). Bone marrow
biopsy reveals a plentiful supply of platelet-producing megakaryocytes (the
giant cells of bone marrow give origin to blood platelets).
Treatment
The behaviour of the disease is different in
children and adults. In children, the disease regresses spontaneously in 75 per
cent of cases after one attack. Short courses of corticosteroids or
occasionally azothiaprine are usually followed by recovery. Splenectomy is
reserved for severe cases which have relapsed or girls approaching menarche. In
adults, the initial attack is less severe than in children, but the disease
relapses and becomes more severe. Splenectomy is indicated where the ITP has
persisted for more than 6—9 months.
Sixty
per cent of patients can be regarded as cured, 20 per cent will be improved and
15 per cent or more will derive no benefit from the splenectomy. It is often,
although not invariable, that a response to steroids predicts a
good response to splenectomy. If severe bleeding has not been controlled by
steroids, fresh blood transfusion or transfusion with platelet concentrates
before operation is often necessary. Splenectomy is contraindicated during the
acute phase of ITP; the disease should first be controlled by medical treatment.
Occasionally, in resistant cases, the antiplatelet immune response can
temporarily be blocked by IgG transfusion to saturate the splenic Fe binding
sites and reduce platelet destruction to allow the platelet count to rise at the
time of surgery.
Splenectomy
for other causes of thrombocytopenic purpura
Occasionally, splenectomy is of benefit in
thrombocytopenia due to systemic lupus erythematosus and in hypersplenism; also
in purpura associated with points 3c and 3d above.