What Is Miliary Tuberculosis?
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Medically reviewed by Susan Russell, MD
Miliary tuberculosis (TB), also known as disseminated TB, is a rare but potentially fatal complication of TB, most often affecting infants and children younger than 5 as well as people with weakened immune systems.
This disease arises when the infecting bacteria, Mycobacterium tuberculosis, enter the bloodstream, spreading to the lungs and other organs. It causes tubercles, small growths the size of millet seeds, to form in the lungs and leads to a wide range of symptoms, depending on the organs it affects.
This article discusses the symptoms, causes, diagnosis, and treatment of miliary TB.
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Types of TB
There are two primary types of TB infection. About 30% of people exposed to M. tuberculosis infected develop latent TB, meaning they have no symptoms and are not contagious. Of these people, about 5 to 10% develop active, or symptomatic, TB. Only specific medical tests can detect latent TB and screening is recommended for anyone at greater risk of exposure to TB.
Active TB, the more serious type, is when you experience signs of the condition. Typical symptoms of this form, a precursor to miliary TB, include chronic cough or coughing blood or sputum (thick, colored mucus), weakness or fatigue, chills, and fever, among others.
Why is it called miliary TB?
The term “miliary” comes from the most prominent feature of this complication: the development of millet seed-sized growths (tubercles) in the lungs, which are visible in chest X-rays.
Miliary TB Symptoms
Because miliary TB represents infection spread, it causes many symptoms specific to the affected organs. The most common are those of active TB and include:
Persistent cough for three weeks or longer
Coughing up blood or sputum
Fatigue and weakness
Loss of appetite (anorexia)
Additional symptoms arise as miliary TB spreads to organs beyond the lungs. These vary based on the affected area. Here's a breakdown:
Tuberculous meningitis: This form of TB occurs when the infection spreads to the tissues surrounding the brain or meninges, causing inflammation. Meningitis leads to headaches, fever, stiff neck, vomiting, behavioral changes, irritability, and other symptoms.
Choroidal tubercles: Choroidal tubercles are growths within the choroid, part of the middle layer of the eye, or uvea, caused by TB bacteria. Typically affecting one eye at a time, this issue can affect vision.
Skin lesions: Also known as cutaneous lesions, this form of TB spreads to skin tissues and causes the development of red or yellow bumps (papules and nodules). These bumps are fragile and painful to the touch and can develop into ulcers.
Bone marrow TB: Infection spreading to the marrow (the tissues inside the bone) can also cause serious issues. Though asymptomatic in its early stages, advanced forms lead to pain (often in the spine), swelling, stiffness, or the development of abscesses, among other complications.
Liver infection: Infection that has spread to the liver can lead to jaundice, a yellowing of the skin and eyes, resulting in liver inflammation. It may cause symptoms like abdominal pain, vomiting, unusually colored or pale stools, and dark or brownish urine.
Adrenal insufficiency: If the adrenal glands, small triangular glands just above the kidneys, become infected, adrenal insufficiency, or Addison's disease, can arise. This dysfunction affects the adrenal glands' ability to produce essential hormones, causing fatigue, nausea, darkening of the skin, low blood pressure, and other symptoms.
Causes
When a person with an active, symptomatic case of TB coughs, sneezes, speaks, or sings, they expel tiny, infected droplets into the air. The bacteria spreads when people breathe in these droplets. As such, TB is an airborne infection that most often spreads between people with frequent close contact.
Routes of Transmission
TB doesn't spread by touching skin, sharing food or drink, kissing, or touching the surfaces of bedding where those affected have slept. Only those with active lung or throat symptoms are contagious with this disease.
In contrast to latent TB or primary active forms, miliary TB occurs when the infection spreads to other body parts via the blood, primarily due to diseases or conditions that cause weakened immune function. Among the risk factors for developing this condition are:
Age below four or above 65
Cancer
End-stage kidney failure
Taking immunosuppressive drugs, such as corticosteroids, biologics, and others
Organ transplant or major surgery
Diagnosis
Though severe, miliary TB can be difficult to diagnose because its presentation varies based on the affected body system. Generally, TB is detected through clinical evaluation, medical tests, and imaging methods to isolate cases. These include:
Medical assessment: Your healthcare provider will review your medical history, medications you are taking, symptoms, and overall health status.
TB skin test: Evaluating your skin’s reactions to injection with a special fluid called tuberculin can determine the presence of TB. After 48–72 hours, a provider will analyze the skin around the injection site, looking for evidence of infection.
TB blood test: Two clinical blood tests, the QuantiFERON-TB Gold Plus (QFT-Plus) and the T-SPOT.TB (T-Spot), are approved for use in the United States to diagnose TB. These tests require clinical evaluation of blood samples to detect antigens, chemicals released by blood cells when fighting off infection.
Chest X-ray: Images from chest X-rays can evaluate TB that’s affecting the lungs. Millet seed-sized lesions—one of the chief characteristics of miliary TB—are prominent in imaging.
Sputum smear: Signs of a TB infection also occur in your saliva. A clinical assessment of a sample can help physicians confirm the diagnosis.
Additional tests are required to confirm the spread of the disease, indicating miliary TB, including:
Fundus examination: To assess for choroidal tubercles in the eyes, a physician dilates the eye with a particular chemical and assesses the interior using a special instrument called an ophthalmoscope. This test is also part of the standard eye exam.
Cytopathology: A healthcare provider, often a specialist called a pathologist, takes a small tissue sample to evaluate under a microscope. They look for a specific type of cell to see if the TB has spread to other internal organs, such as the liver. Your provider may use a long needle (fine needle aspiration) or instruments to scrape off small tissue samples or work from bodily fluids samples.
Biopsy: Similar to cytopathology, a biopsy involves assessing a broader range of cell types taken from specific organs using a microscope. It can confirm TB in the lungs, lymph nodes, bone marrow, or other organs in the body.
Bone marrow aspiration: A provider uses a specialized needle and small incision to remove a small sample of bone marrow liquid and sends it to a laboratory for clinical evaluation.
Treatment
Miliary TB is treated like other active types, with extended courses of antibiotic drugs, taken daily or weekly, lasting between six and 12 months. Specific methods of treatment vary based on the organs affected and the presence of HIV/AIDS, cancer, or other diseases.
Often used in combination, medications for TB include:
Rifadin (rifampin)
Isoniazid
Pyrazinamide
Ethambutol
Streptomycin
In cases of miliary TB complications like adrenal insufficiency, meningitis, acute respiratory distress syndrome (ARDS), and pericarditis (the inflammation of heart tissues), corticosteroids can augment therapy.
Prognosis
Though miliary TB is rare—arising in only about 1% of active cases—it can become severe. Studies have found that the chances of death within a year approach 100% if left untreated. However, therapies for miliary TB are effective in approximately 90% of cases. Though challenging, treatments have proven effective in taking on this condition.
Summary
Miliary tuberculosis is a rare complication of TB, a bacterial infection that is contagious when a person with TB is symptomatic. Occurring when the infecting bacteria enters the bloodstream and spreads to other parts of the body, it’s most often seen in those with weakened immunity and children or infants under the age of 4. This condition leads to a wide range of symptoms and is fatal if untreated. Prolonged courses of antibiotic therapy treat the infection and resolve most cases.
