Idiopathic CD4 Lymphocytopenia

Idiopathic CD4 lymphocytopenia is a persistent low CD4 T cell count (under 300 cells/microlitre, or under 20% of T cells) on at least two occasions 6 weeks or more apart, with a negative HIV test and no other cause. It carries a risk of opportunistic infection and autoimmunity.

Pathophysiology. The cause is heterogeneous: reduced production, increased apoptosis, redistribution, or autoantibodies against T cells. Some patients carry variants in genes that regulate T cell function, and others have no known cause.

It is rare. Most patients are adults, and it affects both sexes.

The count may stay stable for years, fall slowly or recover.

• Opportunistic infection: cryptococcal meningitis, Pneumocystis pneumonia, progressive multifocal leukoencephalopathy, non-tuberculous mycobacteria, histoplasmosis
• Persistent HPV disease (warts, cervical neoplasia), molluscum contagiosum, herpes zoster
• Oral and genital candidiasis
• Autoimmune disease: lupus, thrombocytopenia, thyroid disease, arthritis
• Lymphoma and other malignancy
• Many patients have no symptoms and are found on testing

• CD4 count by flow cytometry, repeated at least 6 weeks later, with a total lymphocyte subset panel (CD3, CD8, CD19, CD16/56).
• HIV testing: fourth generation antigen and antibody test, with HIV RNA PCR if there is doubt. Test for HIV-2 and HTLV-1 and 2.
• Exclusion of secondary causes: drugs (corticosteroids, chemotherapy, azathioprine, interferon), cancers, sarcoidosis, systemic lupus erythematosus, Sjögren syndrome, radiation, malnutrition, and alcohol.
• Immunoglobulins and specific antibody responses.
• Genetic testing for T cell defects when onset is early or there is a family history.
• Infection workup directed by symptoms: serum cryptococcal antigen, CMV and EBV PCR, imaging.

Differential diagnosis.

• HIV infection and HTLV infection
• Secondary CD4 lymphopenia (drugs, sarcoidosis, lupus, lymphoma)
• Combined immunodeficiencies, such as GATA2 and DOCK8 deficiency
• Common variable immunodeficiency
• Thymoma associated immunodeficiency (Good syndrome)
• Physiological lymphopenia with acute stress or infection

• Pneumocystis prophylaxis when CD4 is under 200 cells/microlitre: co-trimoxazole 960 mg orally three times weekly or 480 mg daily (reduce at creatinine clearance under 30 mL/min). Stop only after CD4 counts rise over 200 for at least 3 months.
• Treat infection by organism:
  • Cryptococcal meningitis: liposomal amphotericin B 3 to 4 mg/kg intravenously daily with flucytosine 25 mg/kg orally four times daily for 2 weeks (adjust to renal function and monitor blood count), then fluconazole 400 to 800 mg orally daily for 8 weeks, then 200 mg daily for at least 1 year. Control intracranial pressure by lumbar puncture when raised.
  • Pneumocystis pneumonia: co-trimoxazole with trimethoprim 15 to 20 mg/kg daily in 3 to 4 divided doses, intravenously or orally, for 21 days (halve at creatinine clearance 15 to 30 mL/min), with prednisolone for hypoxaemia (PaO2 under 9.3 kPa): 40 mg twice daily for 5 days, then 40 mg daily for 5 days, then 20 mg daily for 11 days.
  • Non-tuberculous mycobacteria: clarithromycin 500 mg twice daily, ethambutol 15 mg/kg daily and rifampicin 10 mg/kg daily (maximum 600 mg) for at least 12 months after cultures turn negative.
• Immunoglobulin replacement only for coexisting antibody failure with infections: intravenous immunoglobulin 400 to 600 mg/kg every 3 to 4 weeks, or subcutaneous immunoglobulin 100 to 150 mg/kg weekly.
• Warts and HPV: 9-valent HPV vaccine, cryotherapy, imiquimod 5% cream three times weekly at night for up to 16 weeks, and yearly cervical or anal cytology.
• Autoimmunity: treat in the usual way; avoid drugs that lower CD4 counts further when possible.
• Vaccines: inactivated influenza, pneumococcal conjugate and COVID-19 vaccines; avoid live vaccines when the CD4 count is under 200 cells/microlitre.
• Haematopoietic stem cell transplantation for severe, progressive disease with a defined genetic defect.
• Interleukin-2 and interleukin-7 have been used experimentally and are not established treatments.

Special groups.

• Patients from regions with high rates of HIV, tuberculosis and cryptococcosis: repeat HIV testing after any risk exposure and screen for latent tuberculosis.

Monitoring. CD4 count every 3 to 6 months. Full blood count, liver enzymes and creatinine every 6 months. Cervical or anal cytology yearly. Vigilance for new fever, headache, cough or weight loss.

Referral and escalation. Refer to immunology and infectious diseases. Emergency for headache with fever, confusion, or breathlessness with low oxygen saturation.