Thrombocytopaenia and thyroiditis: coincidence?

Abstract

Thrombocytopaenia can be associated with an autoimmune mechanism. Immune thrombocytopaenia can be associated with thyroid autoimmune disease. The authors present a case of a teenager with a history of thrombocytopaenia who complained of tiredness. Laboratory investigation showed thyroid autoantibodies. The co-existence of thrombocytopaenia and thyroiditis lead to further investigation and antibodies against platelet glycoprotein IIbIIIa were found. This case illustrates the association of the overlap aspects between thyroid and platelet autoimmunity.

Background

Immune thrombocytopaenia (ITP) is characterised by persistent thrombocytopaenia (platelet count <100×10⁹/L) and can be classified as primary or secondary, the latter occurring in association with a disease/abnormality that may remain unrecognised in asymptomatic patients. In primary ITP, most patients have antibodies against integrin αIIbβ3 (glycoprotein IIb/IIIa), glycoprotein Ib/IX or other platelet proteins. A small percentage of the normal population may present platelet-associated anti-GPIIb/IIIa antibodies.¹ The association between ITP and autoimmune thyroid disease has been discussed and analysed in several studies.

Case presentation

A previously healthy 16-year-old girl admitted to the emergency department for tiredness, dizziness and nausea for 1 month. General examination was unremarkable; in particular, there were neither skin lesions, visible blood loss or palpable lymphadenopathy and thyroid examination showed no changes. Laboratory tests showed haemoglobin 143g/L, haematocrit 43.3%, thrombocytopaenia (59x10⁹/L), leucopenia (2900/µL), 27.5% monocytes and the morphological study of the peripheral blood confirmed thrombocytopaenia and leucopenia with no other alteration. Leucopenia and monocytosis were interpreted in the context of a viral infection that the adolescent presented concomitantly. There was no evidence of another disease process causing bicytopaenia or pancytopaenia. No specific treatment was given. The adolescent was sent to paediatric consultation for further investigation.

Investigations

After 3 weeks, leucopenia and monocytosis were no longer present, with thrombocytopaenia persisting. The thyroid function (thyroid-stimulating hormone and free T4) was normal, serum thyroid antibodies were present: microsomal antibodies: 203.00 UI/mL (reference value (RV) <5.61 UI/mL) and thyroglobulin antibodies: 14.24 UI/mL (RV <4.11 UI/mL). Anti-platelet antibody screening, by an ELISA immuno-assay, was performed in serum and plasma with positive results against the platelet glycoprotein IIb/IIIa (human platelet antigen (HPA) 1a); an autoantibody because, in platelet genotyping, the patient is HPA 1a/a (relative to platelet antigen 1). Thyroid ultrasound was performed and showed a gland of normal size, with heterogeneous pattern and presence of pseudo nodules, suggestive of thyroiditis. The additional laboratory investigation, after 3 months, was normal except for platelet count (83 000/µL). No medication was given.

Outcome and follow-up

Periodic medical surveillance is maintained, with annual imaging and analytical re-evaluation every 6 months. Eighteen months after the diagnosis, the patient is asymptomatic; platelet count is 83 000/µL; thyroid function remains normal, microsomal antibodies: 317.00 UI/mL (RV <5.61 UI/mL), thyroglobulin antibodies: 18.85 UI/mL (RV <4.11 UI/mL) and there is no detectable thyroid abnormality on ultrasound.

Discussion

In this case, the initial complaint of tiredness led to a blood test, which revealed thrombocytopaenia, which corresponded to an unexpected finding. In the situation of thrombocytopaenia, a correct investigation is crucial because manifestations of an associated disease may not always be present and it can be misclassified as primary thrombocytopaenia. Family history positive for autoimmune diseases must be taken into account. It is known that systemic autoimmune diseases are associated with the development of ITP.² The association between autoimmune thyroid disease and ITP remains in debate and several studies have been published. The studies reporting associations between ITP and clinical/subclinical thyroid autoimmune diseases suggest an overlap between thyroid and platelet autoimmunity.³ This combination seems to indicate a more significant defect in immune tolerance and this subgroup of patients are more refractory to ITP therapy.^4–6

Author’s objective presenting this case is to alert to the overlap aspects between thyroid and platelet autoimmunity and to remember that patients with ITP should be screened for thyroid autoantibodies.

Learning points.

• Systemic autoimmune diseases are associated with immune thrombocytopaenia (ITP).

• Autoimmune thyroid diseases are frequently associated with autoimmune diseases of other organs.

• Recent studies report an association between ITP and thyroid autoimmune diseases, clinical and subclinical.

• With or without clinical manifestations, patients with ITP in the absence of a cause should be screened for thyroid autoantibodies.

• Further studies are necessary to study the impact of treating thyroid diseases in the clinical course and the results of ITP.