A18.81 Tuberculosis of thyroid gland

Name of the Condition

• Tuberculosis of thyroid gland
• ICD Code: A18.81

Summary

Tuberculosis of the thyroid gland is a rare form of extrapulmonary tuberculosis where Mycobacterium tuberculosis infects the thyroid gland. This condition occurs when TB bacteria spread from a primary site, typically the lungs, to the thyroid via the bloodstream or lymphatic system. It may present as a nodule, goiter, or thyroid dysfunction, depending on the extent of infection and tissue involvement.

Causes

Tuberculosis of the thyroid gland is caused by the dissemination of Mycobacterium tuberculosis from an existing infection, usually pulmonary tuberculosis. The bacteria can travel to the thyroid during active disease or reactivation of latent TB. Direct inoculation is rare but possible in certain cases.

Risk Factors

• Immunocompromised states, such as HIV/AIDS or chronic steroid use.
• History of untreated or inadequately treated tuberculosis.
• Close contact with individuals who have active TB.
• Living in or traveling to regions with high TB prevalence.
• Underlying conditions like diabetes or malnutrition.

Symptoms

• Thyroid nodule or swelling, which may be painless or tender.
• Hoarseness or voice changes.
• Difficulty swallowing (dysphagia) if the gland is enlarged.
• Symptoms of hypothyroidism or hyperthyroidism, depending on gland function.

Diagnosis

Diagnosis involves a combination of clinical evaluation, imaging (e.g., ultrasound), and laboratory tests. Fine-needle aspiration or biopsy of the thyroid nodule may be performed to detect Mycobacterium tuberculosis via culture, PCR, or histopathology. Additional tests, such as thyroid function studies, may assess glandular function.

Treatment Options

Treatment typically follows standard anti-tuberculosis regimens, including a combination of antibiotics (e.g., isoniazid, rifampin, pyrazinamide, and ethambutol) for 6–9 months. Thyroid function should be monitored, and hormone replacement therapy may be necessary if hypothyroidism develops.

Prognosis and Follow-Up

With appropriate treatment, the prognosis is generally good, though recovery may take several months. Follow-up includes monitoring for treatment response, thyroid function, and potential recurrence. Long-term surveillance is recommended to ensure complete resolution and address any residual thyroid dysfunction.

Complications

• Chronic thyroid dysfunction (hypothyroidism or hyperthyroidism).
• Abscess formation or fistula development.
• Spread of infection to adjacent structures.
• Rarely, life-threatening systemic TB if not treated promptly.

Lifestyle & Prevention

• Adhere to prescribed anti-TB medications to prevent resistance.
• Maintain good nutrition and overall health to support immune function.
• Avoid close contact with individuals who have active TB, especially if immunocompromised.
• Follow public health guidelines for TB prevention in high-prevalence areas.

When to Seek Professional Help

Seek medical attention if you experience persistent thyroid swelling, voice changes, difficulty swallowing, or unexplained weight changes. Prompt evaluation is critical if you have a history of TB or are at high risk for reactivation.

Tips for Medical Coders

Code A18.81 is specific to tuberculosis of the thyroid gland. Documentation should clearly indicate the site of infection and confirm the diagnosis, typically through biopsy or microbiological testing. Ensure the code is not used for other thyroid conditions (e.g., autoimmune or neoplastic) without supporting evidence of TB involvement.