eMedicine Specialties > Ophthalmology > Infectious Disease

Tuberculosis: Differential Diagnoses & Workup

Author: Pamela S Chavis, MD, Associate Professor, Department of Ophthalmology, Consulting Staff, Department of Neuro-Ophthalmology, Medical University of South Carolina
Coauthor(s): Susannah K Mistr, MD, Resident Physician, Department of Ophthalmology, University of Maryland Medical Center
Contributor Information and Disclosures

Updated: Nov 7, 2008

Differential Diagnoses

Other Problems to Be Considered

Rheumatoid arthritis

Workup

Laboratory Studies

• The primary screening and diagnostic test is the tuberculin skin testing with purified protein derivative (PPD) or intermediate strength purified protein derivative (IPPD). Control skin testing with another antigen, such as Candida, may be considered to validate the PPD or IPPD.
  • The tuberculin skin test is available in the following 3 strengths: 1 tuberculin unit (TU) (low strength for highly sensitive individuals), 5 TU (standard or intermediate strength), and 250 TU (for highly anergic individuals, not to be used for initial injection).
  • The PPD test is given in an intracutaneous injection, preferably with a 26-, 27-, or 30-gauge needle. Comparison can be made with simultaneous Candida or mumps control intracutaneous injections to rule out anergy. These dermal delayed-type hypersensitivity tests should be read within 48-72 hours after administration.
  • Qualified health care personnel can interpret the skin testing results. Any palpable induration measuring 10 mm or more is considered a positive reaction. A doubtful reaction measures 5-9 mm and might also be caused by previous bacille Calmette-Guérin (BCG) immunization in a person with normal immune responses. Exposure to atypical mycobacteria, especially in farm workers, also may produce a doubtful reaction. Five millimeters or more induration in a patient exposed to known active TB, particularly with a previously known negative response, should be considered positive. A negative response in immunologically intact individuals measures less than 5 mm. Repeat testing may cause a booster effect and false-positive results. Interpretation of equivocal testing and repeat administration with the same or higher concentrations of PPD can be left to pulmonary or infectious disease physician consultants.
• Culture for acid-fast bacilli (AFB) is the most specific and allows direct identification and susceptibility of the causative organism; however, access to the organisms may require lymph node/sputum analysis, bronchoalveolar lavage, or aspirate of cavity fluid or bone marrow. Unfortunately, obtaining the test results is slow (3-8 wk), and they have a very low positivity in intraocular disease. AFB stain is quick but requires a very high organism load for positivity. This is more useful in patients with pulmonary disease, but a delay in diagnosis can increase mortality, as other diagnostic testing may need to be considered.
• Refinement in molecular techniques has helped with the diagnosis of intraocular TB. Polymerase chain reaction (PCR) of subretinal fluid has been successful in identifying the presence of TB in cases where the culture result is negative. Nested-PCR further reduces the antigen density required to obtain a positive result but comes with an increased risk of false positivity.
• Enzyme-linked immunosorbent assay (ELISA) evaluates host immunoglobulin G (IgG) and immunoglobulin M (IgM) levels and can help identify recent infection but is not a particularly sensitive test.
• See related CME at Options for Screening and Treatment of Tuberculosis Reviewed.

Imaging Studies

• Obtain a chest x-ray to evaluate for possible associated pulmonary findings. A traditional lateral and PA view should be ordered in addition to the more sensitive apical lordotic view, which permits better visualization of the hyperoxygenated apices and increases the sensitivity of the chest x-ray for indolent or dormant disease. The chest film is also useful to screen for sarcoidosis, which closely imitates the clinical course of ocular TB. Radiologists look more decisively for signs of TB or sarcoid if the requesting physician simply asks to rule out sarcoid or TB.
• CT scan would be desirable to evaluate for a possible orbital mass from TB, but the results are nonspecific for the disease.
• Optical coherence tomography (OCT) of choroidal lesions highlights an elevated choroid with localized contact of the choriocapillaris-retinal pigment epithelial complex with subretinal fluid.

Other Tests

• More recently developed assays may be used to augment the PPD test. Interferon gamma titers correspond to the strength of PPD and appear to correlate more strongly to the risk of disease than PPD. This test is not confounded by BCG exposure since it relates to proteins found in M tuberculosis but not in BCG. However, immunosuppressed patients may yield inconclusive/negative results and positive tests can occur in latent TB.

Procedures

• See Histologic Findings.

Histologic Findings

Biopsy of the eye or ocular tissue is rarely required. The specimen would be expected to demonstrate caseating granuloma. Organisms are rarely obtained from ocular samples.

• Search for CME/CE on This Topic »

• Tuberculosis (Pediatrics: General Medicine)
• Tuberculosis of the Genitourinary System (Urology)
• Tuberculosis (Infectious Diseases)
• Epididymal Tuberculosis (Urology)
• Lung, Primary Tuberculosis (Radiology)

• Bacterial and Viral Infections Center
• Tuberculosis Causes
• Tuberculosis Overview
• Tuberculosis Symptoms
• Tuberculosis Treatment

• Tobacco Smoking May Increase Risk for Tuberculosis
• New Test Identifies Active Tuberculosis Rapidly and Accurately
• Immunosuppression, M. Tuberculosis Commonly Associated With Splenic Abscess

• Emerging Drugs for Active Tuberculosis
• Tuberculosis Disparity between US-born Blacks and Whites, Houston, Texas, USA
• Tuberculosis Reactivation During Immunosuppressive Therapy in Rheumatic Diseases: Diagnostic and Therapeutic Strategies