Camelidae and Cervidae Lymphoma – NAVLE Study Guide

Overview and Clinical Importance

Lymphoma (lymphosarcoma) is the most commonly diagnosed neoplasia in camelids (llamas and alpacas) and represents an important, though sporadic, condition in cervids (deer, elk, moose). This malignancy of lymphoid tissue presents unique diagnostic and therapeutic challenges in these species due to limited research, variable clinical presentations, and the scarcity of established treatment protocols. Understanding the species-specific characteristics of lymphoma is essential for NAVLE success and clinical practice with these increasingly popular animals.

Lymphoma accounts for approximately 18% of all neoplastic and proliferative diseases in camelids, making it the single most common tumor type. Notably, alpacas are significantly overrepresented compared to llamas, with studies showing alpacas comprising up to 75% of diagnosed lymphoma cases. The disease tends to occur at a younger age in camelids compared to other domestic species, with particular prevalence in animals under 5 years of age.

Etiology and Pathophysiology

Camelid Lymphoma

The exact etiology of lymphoma in camelids remains unknown, but several factors have been investigated. Unlike bovine lymphoma, which has a known viral etiology (Bovine Leukemia Virus), camelid lymphoma does not appear to be routinely associated with BLV infection, though a single case report has documented BLV-associated lymphoma in an alpaca. The high prevalence in alpacas and in younger animals suggests a possible genetic predisposition, similar to patterns observed in certain dog breeds and in human pediatric populations.

Malignant round cell tumors (MRCT) in camelids represent a heterogeneous group that includes lymphoma, primitive neuroectodermal tumors (PNET), and other poorly differentiated tumors. This heterogeneity necessitates immunohistochemistry for accurate diagnosis and classification.

Cervid Lymphoma

Lymphoma in cervids (deer, elk, moose) is sporadic and relatively rare compared to other ruminant species. Multicentric lymphosarcoma has been reported in white-tailed deer, European roe deer, water deer, and other cervid species. The etiology is largely unknown; while BLV can experimentally induce lymphoma in some species, it has not been definitively linked to naturally occurring cervid lymphoma.

Primary central nervous system (CNS) lymphoma has been documented in cervids, presenting with neurological signs such as ataxia, circling, and behavioral changes. This presentation creates an important differential diagnosis consideration alongside Chronic Wasting Disease (CWD), which is a major concern in cervid populations.

Species Comparison: Lymphoma Characteristics

Clinical Signs and Presentation

Camelid Lymphoma

Clinical signs in camelids are highly variable depending on organ involvement. The disease course can range from sudden death to a protracted illness lasting weeks. Importantly, animals 2 years of age or younger tend to have a more rapid clinical course (less than 2 weeks from onset to death in most cases).

Common Clinical Findings

• Anorexia - Most common presenting complaint
• Recumbency or weakness - Progressive lethargy
• Weight loss or poor growth - Especially in crias
• Peripheral lymphadenomegaly - Present in only 7 of 24 animals in one study; often detected at necropsy rather than clinical exam
• Respiratory distress - Dyspnea, inspiratory noise if tracheal/thoracic involvement
• Soft tissue masses - May be palpable in ventral cervical region

Cervid Lymphoma

Clinical signs in cervids depend on the anatomical form and affected organs:

• Multicentric form: Lymphadenopathy, multifocal masses affecting heart, blood vessels, kidney, urinary bladder, peritoneum
• Primary CNS form: Ataxia, circling, behavioral changes (loss of timidity), claudication, paralysis
• Subcutaneous form: Palpable masses (e.g., maxillary, submandibular)

Diagnostic Approach

Clinical Pathology Findings

Laboratory abnormalities in camelids with lymphoma are variable and nonspecific, but several patterns have been identified:

Diagnostic Imaging

Ultrasonography: Abdominal ultrasound is valuable for detecting hepatic and splenic involvement. The liver is commonly affected in camelids with lymphoma, and careful evaluation of hepatic parenchyma is recommended. Ultrasonography detected tumors in 4 of 6 animals examined in one study.

Radiography: Thoracic radiographs may reveal mediastinal masses or pulmonary involvement. Cervical radiographs can identify tracheal narrowing due to compressive masses.

CT/Advanced Imaging: Computed tomography provides superior evaluation of disease extent, presurgical planning, and assessment of intraluminal vs extraluminal components of masses. CT is the gold standard for tracheal neoplasm evaluation in human medicine.

Cytology and Histopathology

Fine Needle Aspiration (FNA): Cytologic evaluation of lymph node aspirates, fluid samples, or tissue aspirates was diagnostic in 5 of 6 cases examined in one study. FNA reveals a monomorphic population of large, immature lymphocytes with basophilic cytoplasm, large nuclei, and prominent nucleoli. May see large vacuoles in necrotic cells.

Histopathology: Definitive diagnosis requires histopathologic examination. Lymph node architecture is effaced by sheets of neoplastic lymphoid cells. Nuclear size classification (small, intermediate, large) is important for subtyping.

Immunophenotyping

Immunohistochemistry (IHC) is essential for accurate classification of malignant round cell tumors in camelids. Because signalment, clinical findings, and gross pathology are indistinguishable between lymphoma types and other MRCTs (primitive neuroectodermal tumors), immunophenotyping is critical for diagnosis and prognosis.

Treatment Options

Chemotherapy in Camelids

Reports of chemotherapy for malignant round cell tumors in camelids are rare and outcomes are generally poor. The limited literature includes:

• COP Protocol: Cyclophosphamide, vincristine (Oncovin), and prednisolone combination was attempted in a llama with multicentric lymphoma. Response was transient and short-duration only.
• Surgical excision: May be considered for solitary lymphoma (rare presentation). One successful surgical treatment of a solitary T-cell lymphoma in the ventral cervical region of a llama has been reported.

Chemotherapy Protocol Comparison (Adapted from Canine Protocols)

Prognosis

Prognosis for lymphoma in camelids and cervids is generally poor to grave. Key prognostic factors include:

• Age at diagnosis: Animals 2 years or younger have more rapid disease progression
• Anatomical form: Multicentric disease carries worse prognosis than solitary tumors
• Immunophenotype: In other species, T-cell lymphoma generally has poorer prognosis than B-cell
• Stage at diagnosis: Disseminated disease at diagnosis indicates poor outcome

In one study of 24 camelids with MRCT, all but 1 animal died or was euthanized. Clinical course of 2 weeks or less prior to death was more common in animals 2 years of age or younger (9/11 = 82%) than in older animals (6/13 = 46%).

Differential Diagnoses

Camelids with Lymphadenomegaly

• Caseous lymphadenitis (Corynebacterium pseudotuberculosis)
• Tuberculosis (Mycobacterium bovis)
• Reactive lymphoid hyperplasia
• Other neoplasia (squamous cell carcinoma with metastasis)

Cervids with Neurological Signs

• Chronic Wasting Disease (CWD) - Critical differential; prion disease
• Rabies
• Meningeal worm (Parelaphostrongylus tenuis)
• Brain abscess
• Listeriosis

Prevention and Early Detection

While prevention of lymphoma is not currently possible, early detection may improve outcomes:

• Regular physical examinations: Annual in adults; more frequent (every 6 months) in animals under 2 years
• Lymph node palpation: Careful evaluation of mandibular and inguinal nodes at every exam
• Baseline clinicopathology: Routine CBC and chemistry may detect early abnormalities
• Abdominal ultrasound: Consider if hypoalbuminemia, anemia, or abnormal hepatic enzymes detected