Exotis ISSN 2398-2985

Ferrets

Splenomegaly

Synonym(s): Enlargement of the spleen

Contributor(s): Cathy Johnson-Delaney, David Perpinan

Introduction

  • Cause: extramedullary hematopoiesis (EMH), neoplasia, heart failure accompanying splenic congestion, splenitis, cysts, splenosis, and hypersplenism.
  • Signs: generally asymptomatic, but animals with profound splenomegaly may exhibit decreased activity or gait abnormalities due to the weight and size of the spleen itself.
  • Diagnosis: laboratory testing, radiography, ultrasonography, FNA/biopsy, surgery.
  • Treatment: splenectomy.
  • Prognosis: guarded.
  • A common finding in ferrets.

Pathogenesis

Etiology

  • Extramedullary hematopoiesis (EMH).
  • Neoplasia.
  • Heart failure accompanying splenic congestion, splenitis, cysts, splenosis, and hypersplenism.
  • The ferret spleen can enlarge significantly with anesthesia (injectable and inhalation).
The size of the spleen should always be carefully evaluated in the awake ferret before anesthetized imaging or surgery.

Predisposing factors

General

  • Ferrets are prone to developing splenomegaly.

Pathophysiology

Extramedullary hematopoiesis (EMH)

  • EMH is the most commonly histopathologic diagnosis for ferrets with splenomegaly.
  • EMH represents a compensatory reaction in response to either inadequate bone marrow function or increase blood cell needs. 
  • It may be a result of chronic antigen stimulation or anemia Anemia overview
  • In many cases, the exact disease process resulting in EMH is undetermined.
  • Anemia is assumed to be a potential cause; however ferrets with chronic anemia have been found with normal spleens, and some with enlarged spleens have normal blood counts and bone marrow function.
  • Enlarged spleen size and weight can be induced in laboratory rats after injection of substances noted to produce marked inflammation, lending credibility to the theory that EMH is produced by chronic inflammation in the ferret.
  • Chronic subclinical Helicobacter gastritis Helicobacter mustelae gastritis and other inflammatory gastrointestinal disease is commonly suggested as a possible cause. Chronic subclinical infection with Aleutian disease virus Aleutian disease has also been suggested as a possibility to explain the high incidence of splenomegaly in ferrets. Splenomegaly has also been observed in many animals with canine distemper Canine distemper, systemic coronavirus Ferret systemic coronavirus, etc.
  • EMH is also believed to be responsible for the splenomegaly commonly reported in ferrets with dissemination idiopathic myositis Disseminated idiopathic myofasciitis.

Splenic cysts

  • Cystic structures may be found on palpation or on ultrasound.
  • These are blood filled.
  • It is unknown if they correspond to trauma or neoplastic process.

Splenic neoplasia

  • Lymphoma is the most common neoplasia of the ferret spleen, but other cancers, including hemangiosarcoma, should be considered.
  • Histopathology is recommended to help determine appropriate follow-up treatment and long-term prognosis.

Splenic nodules

  • These may be found upon ultrasound or palpation.
  • The nodules may be fibrotic, congested tissue, or neoplastic.

Splenitis

  • Inflammation of the spleen has been reported in association with ferret systemic coronavirus (FRSCV) Ferret systemic coronavirus, Mycobacterium, or fungal organisms.
  • While many infectious processes can cause enlargement of the spleen due to extramedullary hematopoiesis, cases of true splenitis require the infectious agent to directly infect the spleen.

Ectopic splenic tissue

  • Accessory foci of splenic tissue are occasionally found.
  • Splenic tissue that is found separate from the body of the spleen can either be the result of failure of two sections to fuse during fetal development (accessory spleens) or traumatic/surgical splenic fracture (splenosis):
    • These can be distinguished histopathologically, but typically not by gross appearance.
    • They are typically asymptomatic, but their anatomic position may sometimes predispose them to torsion, rupture, or other complications that result in clinical signs.
  • There is one report of splenosis in a domestic ferret.

Hypersplenism

  • While it is part of the normal function of the spleen to removed damaged or senescent blood cells, in some cases the spleen may perform this function excessively or prematurely.
  • This condition is referred to as hypersplenism and results in an enlarged spleen with anemia and/or leukopenia that resolves with splenectomy.
  • There are several anecdotal reports of this disease in ferrets, but no published case studies.

Epidemiology

  • Splenomegaly is a common condition, yet abnormal, in the ferret.

Diagnosis

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Treatment

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Martorell J, Vrabelova D, Reberte L et al (2011) Diagnosis of an abdominal splenosis in a case of ambulatory paraparesis of the hind limbs in a ferret (Mustela putorius furo). J Exotic Pet Med 20 (3), 227-231 JExoticPetMed.
  • Piseddin E, Trotta M, Tortoli E et al (2011) Detection and molecular characterization of Mycobacterium celatum as a cause of splenitis in a domestic ferret (Mustela putorius furo). J Comp Path 144 (2), 214-218 PubMed.

Other sources of information

  • Swisher S & Lennox A M (2017) Disorders of the Haemic, Immunological and Lymphatic Systems. In: Ferret Medicine and Surgery.  Ed: Johnson-Delaney C A. CRC Press, USA. pp 237-257.


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