Conjunctival lymphoma, a type of ocular adnexal lymphoma, presents a diagnostic challenge due to its varied clinical appearances and overlap with other ocular surface conditions. Establishing an accurate diagnosis is crucial for appropriate management and prognosis. While incisional biopsy remains the gold standard for confirming conjunctival lymphoma, a comprehensive diagnostic approach involves a range of investigations to differentiate it from other benign and malignant conditions. This article delves into the differential diagnosis of conjunctival lymphoma, outlining key investigative modalities and their role in distinguishing this entity from its mimics.
Clinical Examination: Initial Steps in Differentiation
A thorough ophthalmologic examination is the cornerstone of suspecting conjunctival lymphoma. Clinically, conjunctival lymphoma can manifest as a salmon-pink patch, nodule, or diffuse thickening of the conjunctiva. While these signs are suggestive, they are not pathognomonic. Various benign conditions such as conjunctivitis, pinguecula, pterygium, and episcleritis can present with similar symptoms like redness, swelling, and discomfort. Furthermore, benign reactive lymphoid hyperplasia (RLH), a common mimic, can clinically resemble low-grade conjunctival lymphoma. Therefore, clinical examination alone is insufficient for definitive diagnosis but serves to raise suspicion and guide further investigations. Systemic examination is also crucial to assess for any signs of systemic lymphoma involvement.
Imaging Modalities and Differential Diagnosis
Imaging techniques play a supportive role in the differential diagnosis of conjunctival lymphoma, primarily to evaluate the extent of the lesion and rule out orbital involvement or systemic dissemination.
Conventional Imaging (CT/MRI)
Computed tomography (CT) and magnetic resonance imaging (MRI) of the orbits are often employed to assess the retrobulbar extension and laterality of suspected conjunctival lesions. While valuable for orbital lymphoma, studies indicate that clinical examination by an ophthalmologist is often more sensitive than MRI for detecting conjunctival mucosa-associated lymphoid tissue (MALT) lymphoma. MRI enhancement is not consistently present in conjunctival MALT lymphoma, limiting its diagnostic specificity for this condition. However, imaging is warranted when there is uncertainty about whether the lesion is confined to the conjunctiva, as orbital involvement increases the likelihood of associated systemic disease.
PET/CT & PET/MRI
Positron emission tomography/computed tomography (PET/CT) and PET/MRI have emerged as advanced imaging modalities for staging and evaluating lymphoma. Whole-body PET/CT using 18F-fluorodeoxyglucose (18F-FDG) is particularly useful for systemic staging of conjunctival MALT lymphoma and post-treatment evaluation. PET/CT’s sensitivity in detecting distant metastases, even in low-grade disease, surpasses conventional imaging. However, it’s important to note that PET/CT may have limitations in detecting small local ocular adnexal lesions due to physiological tracer uptake by extraocular muscles and the small size of conjunctival lesions. While PET imaging aids in systemic staging and monitoring, it is not a primary tool for differentiating conjunctival lymphoma from other ocular surface lesions.
Optical Coherence Tomography (OCT)
High-resolution optical coherence tomography (HR-OCT) is increasingly valuable in characterizing ocular surface lesions, including conjunctival lymphoma. HR-OCT can reveal distinct tissue morphology and cellular patterns that aid in differential diagnosis. In conjunctival lymphoma, HR-OCT typically shows homogenous, dark subepithelial lesions with smooth borders and monomorphic dot-like infiltrates, correlating to lymphocytic infiltrates histopathologically. A subepithelial hyperreflective band may also be observed. In contrast, benign reactive lymphoid hyperplasia often exhibits more variability in HR-OCT findings, and may lack the hyperreflective band seen in lymphoma. Conjunctival amyloidosis presents as heterogenous subepithelial lesions with irregular borders and hyperreflective opacities. While HR-OCT is limited by shadowing in thick lesions, it is a valuable non-invasive tool for monitoring treatment response and differentiating conjunctival lymphoma from certain benign conditions and amyloidosis based on characteristic morphological features.
Haematological Investigations in Differential Diagnosis
Haematological investigations are crucial in the workup of suspected conjunctival lymphoma, primarily for systemic staging and to exclude systemic lymphoma or related conditions that may mimic conjunctival lymphoma. Serological testing includes a full blood count, biochemistry profile (renal and liver function tests), protein electrophoresis, lactate dehydrogenase (LDH), β2 microglobulin (B2M), and serology for HIV, HBV, and HCV. These tests help assess the patient’s overall health and identify any systemic involvement. Bone marrow aspirate and biopsy are often performed in patients with suspected stage I or II disease, especially when local treatment is planned, to rule out bone marrow involvement, which can alter staging and management.
Histopathological Examination: The Gold Standard for Differentiation
Histopathological examination of an incisional biopsy remains the gold standard for definitive diagnosis and differential diagnosis of conjunctival lymphoma.
Incisional Biopsy and Immunohistochemistry (IHC)
Formalin-fixed, paraffin-embedded tissue sections are stained with haematoxylin and eosin (H&E) to evaluate tumour morphology. Immunohistochemistry (IHC) is essential to characterize the lymphoid infiltrate and differentiate between lymphoma subtypes. IHC panels typically include antibodies against CD3, CD5, CD20, and CD79α to distinguish between T-cell and B-cell lineages. Additional IHC markers are used to further refine the immunophenotype and classify the lymphoma subtype (e.g., MALT lymphoma, diffuse large B-cell lymphoma (DLBCL), follicular lymphoma, mantle cell lymphoma (MCL)).
In conjunctival extranodal marginal zone lymphoma (EMZL), the histology reveals a diffuse monomorphic infiltrate of small B cells in the substantia propria. IHC confirms the B-cell nature and helps differentiate EMZL from other lymphomas. Reactive lymphoid hyperplasia (RLH), a key differential diagnosis, histologically presents as a polymorphous infiltrate with mature lymphocytes, plasma cells, and benign reactive lymphoid follicles with germinal centers. IHC in RLH shows a polyclonal B-cell population, contrasting with the monoclonal B-cell population in lymphoma.
DLBCL, follicular lymphoma, and MCL have distinct histopathological and IHC features that differentiate them from EMZL and RLH. DLBCL is characterized by large, non-cohesive cells with vesicular nuclei, while follicular lymphoma exhibits densely packed follicles. MCL shows a monomorphous population of centrocytes with aberrant CD5 expression and cyclin D1 positivity. T-cell lymphomas, although rare in the conjunctiva, are also considered in the differential diagnosis and require specific T-cell marker IHC evaluation.
Flow Cytometry & Molecular Studies
Flow cytometry on fresh tissue is a valuable adjunct to IHC for immunophenotyping and detecting monoclonality, especially when IHC results are inconclusive or fresh tissue is available. Molecular studies, such as immunoglobulin heavy chain gene rearrangement by polymerase chain reaction (IgH-PCR) and next-generation sequencing (NGS), provide further insights into clonality and genetic features. These techniques are particularly useful in confirming monoclonality, identifying specific genetic aberrations, and aiding in the differential diagnosis, especially in cases where morphology and IHC are ambiguous. Molecular pathology is also increasingly important for identifying potential therapeutic targets and understanding prognosis.
Molecular Pathology: Refining Differential Diagnosis and Prognosis
Molecular pathology plays an increasingly significant role in refining the differential diagnosis of conjunctival lymphoma and understanding disease prognosis. Specific genetic aberrations are associated with different lymphoma subtypes and can aid in distinguishing conjunctival lymphoma from reactive conditions or other lymphomas.
For instance, inactivation of the A20 (TNFAIP3) gene and mutations in MYD88 are observed in conjunctival EMZL and are associated with prognosis. Chromosomal translocations like t(14;18), t(11;18), and t(3;14), though less frequent in ocular EMZL compared to other sites, and trisomies of chromosomes 3, 12, and 18, along with gain of chromosome 6, provide further molecular characterization. Follicular lymphoma is hallmarked by the t(14;18) translocation involving BCL2. In DLBCL, MYC protein alterations and translocations involving BCL2 and/or BCL6 are prognostically relevant. Molecular testing helps to subclassify lymphomas, refine diagnosis, and identify patients who may benefit from targeted therapies.
Differential Diagnoses to Consider
The differential diagnosis of conjunctival lymphoma includes a spectrum of benign and malignant conditions:
- Benign Reactive Lymphoid Hyperplasia (RLH): The most common mimic, clinically and sometimes histologically. Polyclonality and reactive features differentiate RLH from lymphoma.
- Chronic Conjunctivitis: Inflammatory conditions can cause redness and swelling, but lack the mass-forming nature of lymphoma.
- Pinguecula and Pterygium: Common benign conjunctival growths, typically yellowish or fleshy, lacking lymphoid infiltrate.
- Episcleritis and Scleritis: Inflammatory conditions affecting deeper scleral tissues, distinguished by pain and scleral involvement.
- Conjunctival Amyloidosis: Can present as fleshy lesions, but HR-OCT and histology reveal characteristic amyloid deposits.
- Squamous Cell Carcinoma and Melanoma: Malignant epithelial and melanocytic tumors that can mimic lymphoma but have distinct clinical and histopathological features.
- Kaposi Sarcoma: Vascular tumor, more common in immunocompromised individuals, presenting as reddish-purple lesions.
Conclusion
The differential diagnosis of conjunctival lymphoma requires a systematic approach integrating clinical findings, imaging, haematological investigations, and, crucially, histopathological and molecular analyses. While incisional biopsy with IHC remains the gold standard, ancillary tests like HR-OCT, PET/CT, flow cytometry, and molecular pathology provide valuable complementary information for accurate diagnosis, staging, and differentiation from benign and malignant mimics. A multidisciplinary approach involving ophthalmologists, pathologists, and oncologists is essential for optimal patient care and management of conjunctival lymphoma.
