C91.5 Adult T-cell lymphoma/leukemia (HTLV-1-associated)

Name of the Condition

• Adult T-cell lymphoma/leukemia (HTLV-1-associated)
• ICD-10 Code: C91.5

Summary

Adult T-cell lymphoma/leukemia (HTLV-1-associated) is a rare, aggressive cancer of T lymphocytes, a type of white blood cell, caused by the human T-cell lymphotropic virus type 1 (HTLV-1). It involves the uncontrolled proliferation of abnormal T cells, which can affect the blood, lymph nodes, skin, and other organs. The condition may present as leukemia (with high numbers of circulating cancer cells) or lymphoma (with tumor formation in tissues). It is endemic in regions like Japan, the Caribbean, and parts of Africa, and typically affects adults.

Causes

The primary cause is infection with the HTLV-1 virus, which integrates into the host’s T-cell DNA and disrupts normal cell regulation. Genetic mutations in T cells, triggered by the virus, lead to uncontrolled growth. Transmission occurs through blood transfusions, shared needles, sexual contact, or mother-to-child transmission (e.g., breastfeeding). Not all infected individuals develop the disease, suggesting additional host or environmental factors may contribute.

Risk Factors

• Infection with HTLV-1 virus
• Residence in or travel to endemic regions (e.g., Japan, Caribbean, Africa)
• Prolonged breastfeeding in infants of infected mothers
• Blood transfusion or organ transplant from an infected donor
• Intravenous drug use with shared needles
• Sexual contact with an infected partner

Symptoms

• Fatigue and weakness
• Skin rashes or nodules
• Enlarged lymph nodes, liver, or spleen
• Fever, night sweats, or unexplained weight loss
• Neurological symptoms (e.g., weakness, numbness) in some cases
• Elevated calcium levels (hypercalcemia) due to bone involvement
• Frequent infections from impaired immune function

Diagnosis

Diagnosis begins with a physical exam and blood tests to detect abnormal T cells and HTLV-1 antibodies. Flow cytometry or immunophenotyping confirms the presence of malignant T cells. A bone marrow biopsy assesses cellularity and infiltration. Imaging (e.g., CT scans) evaluates organ involvement, and skin or tissue biopsies may be performed if lesions are present. Molecular testing for HTLV-1 integration is confirmatory.

Treatment Options

Treatment depends on disease stage and symptoms. Options include chemotherapy (e.g., CHOP regimen), antiretroviral therapy (e.g., zidovudine), and interferon-alpha. Stem cell transplantation may be considered for eligible patients. Supportive care addresses complications like infections or hypercalcemia. Clinical trials may offer experimental therapies for refractory cases.

Prognosis and Follow-Up

Prognosis is generally poor due to the aggressive nature of the disease, with median survival often less than 1–2 years. Response to treatment varies, and relapse is common. Follow-up includes regular blood tests, imaging, and monitoring for neurological or skin manifestations. Long-term survivors require ongoing surveillance for secondary cancers or viral reactivation.

Complications

• Severe infections from immunosuppression
• Hypercalcemia (elevated blood calcium) leading to kidney damage
• Neurological damage (e.g., myelopathy)
• Organ failure from tumor infiltration
• Transformation to more aggressive lymphoma subtypes
• Viral transmission to others (e.g., through blood or breastfeeding)

Lifestyle & Prevention

• Avoid blood transfusions or organ transplants from untested donors.
• Practice safe sex to reduce HTLV-1 transmission risk.
• Infected mothers should avoid breastfeeding to prevent vertical transmission.
• Limit exposure to shared needles (e.g., through safe injection practices).
• In endemic areas, education on transmission routes may reduce incidence.

When to Seek Professional Help

Seek care if you experience persistent fatigue, unexplained weight loss, skin lesions, or swollen lymph nodes, especially if you live in or have traveled to HTLV-1-endemic regions. Immediate medical attention is needed for symptoms like severe infections, neurological changes, or signs of organ dysfunction (e.g., jaundice, confusion).

Tips for Medical Coders

Code C91.5 is specific to adult T-cell lymphoma/leukemia associated with HTLV-1. Documentation should confirm the viral association (e.g., positive HTLV-1 serology or molecular testing) and specify whether the presentation is leukemia, lymphoma, or both. Ensure the record supports the diagnosis with clinical findings (e.g., abnormal T cells, organ involvement) and excludes other T-cell malignancies.