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232.e2 Cyclic Thrombocytopenia

Cyclic Thrombocytopenia
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postoperative hemorrhage, hyphema, nasal
BASIC INFORMATION
discharge, or lymphadenopathy ○ Possible mild leukopenia
○ Rarely, morulae detected within plate-
Definition lets on blood smear as purple granular
A tick-borne disease of dogs caused by the Etiology and Pathophysiology inclusions
rickettsial agent Anaplasma platys, which causes • A. platys is transmitted during tick feeding. • Serum chemistry: unremarkable
waxing and waning cycles of thrombocytopenia. • Incubation period is approximately 8-15 days • Point-of-care serologic tests (i.e., IDEXX
after tick bite, followed by rapid decline in SNAP 4Dx plus ELISA) can detect A.
Synonyms platelet concentration. phagocytophilum and A. platys (cross-reactive)
• Anaplasma platys (formerly Ehrlichia platys) • Thrombocytopenia results from both but does not differentiate between the two.
infection ○ Direct platelet destruction by multiplying ○ Can help rule out other potential
• Anaplasmosis more often refers to granulocytic organisms inside platelets vector-borne infections that may cause
infection with Anaplasma phagocytophilum ○ Immune-mediated platelet destruction thrombocytopenia (i.e., ehrlichiosis and
(p. 393) • Platelet count recovers and falls every 1-2 borreliosis)
weeks, typically with milder thrombocyto- • Tests of primary coagulation (buccal
Epidemiology penia with each subsequent cycle. mucosal bleeding time) can be prolonged
SPECIES, AGE, SEX • May spontaneously resolve after about 4 but are not considered helpful in the face
• Clinical signs reported in dogs of any age cycles of thrombocytopenia.
and either sex • Bone marrow: normal to megakaryocytic
• The pathogen is detectable in other DIAGNOSIS hyperplasia
species, including cats. However, patho- • Diagnostic imaging of body cavities is
genicity has not been confirmed outside Diagnostic Overview unremarkable but can rule out internal
of dogs. Definitive diagnosis requires serologic con- hemorrhage
firmation of exposure or molecular detection
RISK FACTORS (polymerase chain reaction [PCR]) of the Advanced or Confirmatory Testing
Tick exposure organism in an animal with thrombocytopenia. • PCR is the diagnostic test of choice. The test
Morulae in platelets are rarely detected, and is highly specific; however, false-negatives
CONTAGION AND ZOONOSIS their absence does not rule out infection. may occur (possibly due to low number
• Transmitted primarily by ticks (main vector of circulating organisms at the time of
probably Rhipicephalus sanguineus), but other Differential Diagnosis sampling).
arthropod vectors may play a role. • Other tick-borne diseases, including • Serology by indirect immunofluorescent
• Recent evidence for in utero transmission to ○ A. phagocytophilum antibody test is available through commercial
puppies ○ Ehrlichia canis laboratories.
• Recently, A. platys infection of several humans ○ Ehrlichia ewingii
has been confirmed by molecular detection ○ Rickettsia rickettsii
and visualization of platelet inclusions. Patho- ○ Babesia canis
genicity in people remains to be determined ○ Babesia gibsoni
but is likely low. • Immune-mediated thrombocytopenia
• Bone marrow disease
GEOGRAPHY AND SEASONALITY • Toxin- or drug-induced thrombocytope-
Reported worldwide; seasonality may depend nia (e.g., cisplatin, cyclophosphamide,
on life cycle of the tick vector. chlorambucil, doxorubicin, hydroxyurea,
estrogens)
ASSOCIATED DISORDERS • Disseminated (DIC) or localized (thrombo-
Coinfection with other tick-borne diseases is embolism) intravascular coagulation
common and may result in comorbidities. • Vasculitis
• Canine cyclic hematopoiesis of gray collie
Clinical Presentation dogs
DISEASE FORMS/SUBTYPES • Distemper vaccination can rarely cause
Variants are recognized to have different viru- transient thrombocytopenia
lence. The common variant in North America • Breed-related thrombocytopenia (e.g., King
causes relatively mild to subclinical disease. Charles Cavalier spaniel)
HISTORY, CHIEF COMPLAINT Initial Database
• Usually none (i.e., diagnosis is incidental) • CBC
• Depending on severity of thrombocytopenia: ○ Thrombocytopenia (can vary markedly in
petechiae, ecchymoses, and/or mucosal degree) often with increased mean platelet
hemorrhage volume (MPV) or enlarged platelets CYCLIC THROMBOCYTOPENIA Anaplasma
• Rarely, lethargy and anorexia ○ Possible regenerative anemia secondary to platys organisms in a platelet from a dog with
hemorrhage (usually mild) thrombocytic anaplasmosis (Giemsa stain, ×2500).
PHYSICAL EXAM FINDINGS ○ Repeated cycles (later stage of disease) Inset, Platelet containing morula of A. platys (new
methylene blue; ×2300). (From Harvey JW: Anaplasma
• Usually normal may have mild nonregenerative anemia platys infection [thrombocytotropic anaplasmosis]. In
• Occasionally, pallor, fever, petechiae, (so-called anemia of inflammatory/chronic Greene CE, editors: Infectious diseases of the dog and
ecchymosis, epistaxis, melena, hematochezia, disease). cat, 4 ed, St Louis, 2012, Saunders.)

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