INSTRUCTIVE CASE Beware the lymphopenia: A case of severe combined immunodeficiency Sam Mehr, 1,2 Alyson Kakakios, 1 Peter Shaw, 2,3 Richard Webster 4 and Andrew Kemp 1,2 Departments of 1 Allergy and Immunology, 3 Oncology and 4 Neurology, The Children’s Hospital at Westmead and 2 Children’s Hospital at Westmead Clinical School, Sydney Medical School, Sydney, New South Wales, Australia Abstract: We present a case of a 2-month-old boy with partially treated meningitis and suspected Pneumocystis carinii pneumonia. A full blood count revealed profound lymphopenia. The child was diagnosed with adenosine deaminase deficiency, a rare cause of severe combined immunodeficiency (SCID). SCID is an immunological emergency and must be considered in any lymphopaenic infant with opportunistic infection. We discuss adenosine deaminase-deficient SCID, which can involve multiple systems and in which other treatment options apart from bone marrow transplant are available. Key words: adenosine deaminase; lymphopenia; SCID. Case A 2-month-old boy born at term to non-consanguineous Australian-born parents presented to his local doctor with a week of intermittent fever, rhinorrhoea and diarrhoea. Amox- icillin was prescribed, but 4 days later, he presented to the local hospital febrile (39°C) and irritable. Investigations revealed pro- found lymphopenia (0.1 ¥ 10 9 /L; normal 1.5–3.0 ¥ 10 9 /L), hypoalbuminaemia (24 g/L; normal 30–45) and transaminitis (gamma-glutamyl transferase (GGT) 209 u/L, normal <55; alanine aminotransferase (ALT) 50 u/L, normal <45; aspartate aminotransferase (AST) 100 u/L, normal <35). Cerebrospinal fluid (CSF) white cell count was 20 leucocytes (50% neutrophils and 50% mononuclear cells), protein was 0.86 g/L (normal < 0.4) and glucose was 2.3 mmol/L (normal 3.0–5.0). CSF gram stain and culture, blood culture and stool culture were negative. A provisional diagnosis of partially treated meningitis was made, and intravenous cefotaxime and flucloxacillin were adminis- tered. Four days later, he developed cough with tachypnoea, an oxygen requirement and generalised oedema. A chest X-ray showed an absent thymic shadow and diffuse shadowing across both lung fields (Fig. 1). Pneumocystis carinii (PCP) was sus- pected, and intravenous co-trimoxazole commenced. The child was then transferred to the Children’s Hospital at Westmead, NSW, Australia. Further investigations revealed a low normal immunoglobu- lin G (IgG) (1.7 g/L; normal 1.7–5.8), and normal immunoglo- bulin A (IgA) (0.4 g/L, normal 0.05–1.5) and immunoglobulin Key Points 1 Severe combined immunodeficiency (SCID) must be consid- ered in any infant with opportunistic infection, particularly if associated with lymphopenia. 2 Adenosine deaminase deficiency SCID is a systemic disorder, in which profound lymphopenia and/or non-immune dysfunc- tion are characteristically present. 3 Early diagnosis of SCID is paramount so that a rapid search for a bone marrow donor can be undertaken, because the longer the delay to transplantation, the lower the likelihood of immune reconstitution and survival. Correspondence: Dr Sam Mehr, Department of Allergy and Immunology, The Children’s Hospital at Westmead, Locked Bag 4001, Westmead, Sydney, NSW 2145, Australia. Fax: +61 2 98453421; email: samm@ chw.edu.au Accepted for publication 19 April 2010. Fig. 1 Abnormal chest X-ray with diffuse bilateral shadowing and absence of a thymic shadow. Splaying of the costochondral junctions was also noted (arrows). doi:10.1111/j.1440-1754.2010.01870.x Journal of Paediatrics and Child Health 47 (2011) 565–567 © 2010 The Authors Journal of Paediatrics and Child Health © 2010 Paediatrics and Child Health Division (Royal Australasian College of Physicians) 565