Susan L. Clubb, DVM, Dipl ABVP (Avian), Michael M Garner DVM, Dipl ACVP, and
Carolyn Cray, PhD
Affiliation: From The Rainforest Clinic for Birds & Exotics, PO Box 508, Loxahatchee, FL 33470, USA (Clubb), Northwest ZooPath, 18210 Waverly Drive, Snohomish, WA 98296, USA (Garner), and University of Miami, Division of Comparative Pathology, PO Box 016960 (r-46), Miami, FL 33101, USA (Cray).
Abstract: The etiology of feather picking, chewing or soft tissue mutilation can be difficult to determine. Paired skin biopsies were used to diagnose inflammatory skin disease. In 58 cases where this technique was used, 38% were diagnosed with inflammatory skin disease, and 23% also had low resting plasma levels of thyroxine. The role of hypersensitivity as the cause of inflammatory skin disease is discussed.
Self-destructive behaviors in psittacine birds, such as feather picking or chewing and soft tissue mutilation are common, often multifactoral problems. Establishment of a definitive etiologic diagnosis and effective therapeutic plan is challenging.1,2 In this report, the use of paired skin biopsies was used in order to make a presumptive diagnosis of inflammatory skin disease.
Preliminary results are presented here of a on-going study in which paired biopsies, biopsies of affected and unaffected areas, were evaluated. Fifty-eight individual psittacine birds of 9 genera were included in this study.. Forty of the individuals in this study were also tested for plasma thyroxine levels by radioimmunoassay.
Skin biopsies are frequently recommended as an important diagnostic tool in self-mutilation, plucking, or feather destruction cases.3-5 However, examination of only the affected site provides a limited amount of information upon which to base a diagnosis. Most sites of active plucking or mutilation will exhibit inflammation, even if only associated with self-induced trauma. Examination of an unaffected section of skin allows the pathologist to detect generalized lesions which may be interpreted as inflammatory skin disease and provides circumstantial evidence of hypersensitivity. This is useful in differentiating cases of psychogenic plucking from birds that have generalized hypersensitivity possibly associated with allergies. Following identification of inflammatory skin disease, intradermal skin testing may be useful to pinpoint specific offending allergens.6,7
All cases were randomly chosen from those presented with a complaint of feather plucking, feather destruction, or soft-tissue mutilation. In many cases, other diagnostic tests were also performed. Many of the birds were chronically affected, especially the macaws; however, some were of short duration. Most of the birds were captive-bred and included 38 females (65.5%), 22 males, and 1 bird of unknown sex.
Biopsies were collected under routine isoflourane anesthesia. Growing immature feathers were sampled with a full-thickness section of skin, which included the entire feather follicle. A growing immature feather was selected in an area where the bird was plucking and another was selected in an area which was unaffected, typically the head or neck. The patterns of feather damage were described for future comparison by estimation of amount and type of feather damage in each major body area.
The 58 cases included in this study (grouped by genus) are summarized in Table 1.
Histological changes in 18/58 (38%) of the birds examined were consistent with inflammatory skin disease, which is suggestive of hypersensitivity. Inflammatory skin disease was diagnosed when inflammatory lesions were seen histologically in samples interpreted clinically as “affected” (clinical observations of self trauma) and “unaffected” (sites not observed to be traumatized by the bird). The inflammatory lesions were typically comprised of perivascular infiltrates of low to marked numbers of lymphocytes with fewer plasma cells, histiocytes, and acidophilic granulocytes interpreted as heterophils or eosinophils. Inflammation was sometimes associated with mild perivascular edema. In “affected” sites, inflammation was sometimes associated with epidermal hyperplasia and compact orthokeratotic hyperkeratosis, dermal scarring, perifollicular fibrosis, follicular cysts with hyperkeratosis, furunculosis, feather trauma, and secondary bacterial infection. Cases in which these additional features were present in the “unaffected” specimen disqualified the specimen as primary inflammatory skin disease, because in these cases the inflammation could have been secondary to trauma (undetected clinically) rather than a primary lesion.
The incidence of inflammatory skin disease varied dramatically between genera. High rates were observed in Amazons (Amazona species), macaws (including Ara species), and Eclectus (Eclectus species). The low numbers of birds tested in some genera negate the significance of those findings. Golden conures (Aratinga guarouba or Guaruba guarouba) have an extremely high incidence of feather plucking. Both birds sampled had lesions consistent with inflammatory skin disease. Cockatoos (Cacatua species) and African grey parrots (Psittacus erithacus) showed relatively low rates of inflammatory skin disease (both were 14.3%) but high incidence of low resting thyroxine levels (81% and 100% respectively).
An additional finding study was the high incidence of birds with resting thyroxine levels below reference ranges. Upon analysis of a single resting plasma sample, 27/37 (73%) of birds tested were below reference ranges. The reference ranges (Table 2) used for this comparison were developed by the Comparative Pathology Division of the University of Miami using random samples submitted by practitioners who indicated the birds were clinically normal.
Nine of 40 (23%) birds that were biopsied and also tested for resting thyroxine levels showed concurrent lesions of inflammatory disease and also low resting plasma levels of thyroxine. Pododermatitis in Amazons has been successfully treated with L-thyroxine.3
Hypersensitivity is a type of inflammatory reaction caused by an excessive immunologic response. Four different types of hypersensitivity reactions have been described in mammals. The application of these classifications in birds has been previously reviewed.9-11
Type IV, delayed hypersensitivity is the type typically seen in the skin of mammals. This reaction is caused by cell-mediated immune responses occurring at least 24 hours after antigen contact with sensitized T-cells. The local inflammatory response is caused by vasoactive lymphokines and substances released by mast cells, which in turn attract macrophages. The macrophages can cause tissue destruction and creation of granulomas. This type of reaction can be caused by various bacterial antigens and virus infected cells.9,11
Delayed-type hypersensitivity tests have been used in chickens to measure cell-mediated immunocompetence and is called the delayed wattle test. These reactions can be elicited in birds using tuberculin or contact allergens.11 Histamine is the primary allergic mediator in chickens.11
Hypothyroidism has been loosely associated with feather destruction by numerous authors.1,2,12 10
The biological functions of the thyroid gland in birds include normal molting and development of the plumage. Feather abnormalities which have been associated with hypothyroidism in birds are fringed feathers, loss of barbules, and hypopigmentation of colored feathers; however, more work is needed to fully understand the relationship between thyroid function and normal development and maintenance of plumage.13
The diagnosis of hypothyroidism is based on characteristic clinical signs coupled with the failure to respond to provocative thyroid stimulating hormone (TSH)-stimulation testing. Techniques for provocative testing utilizing TSH have been described.14-17 Only 1 case of hypothyroidism in a psittacine confirmed by TSH-stimulation testing has been reported.18 In this case, the clinical manisfistations of hypothyroidism were similar to those seen in mammals. Obesity and non-puritic feather loss with loss of feather regrowth were evident.
Diagnosis of hypothyroidism in parrots is challenging.13 Clinical signs that have been reported to be associated with low resting serum thyroxine concentrations include lipomas, dry skin, feather picking, and pododermatitis. In these reports, however, the diagnosis of hypothyroidism was not confirmed by TSH stimulation.
A single demonstration of low serum or plasma thyroxine levels must be interpreted with caution because of diurnal and seasonal fluctuations in the activity of the thyroid gland. While provocative testing (TSH stimulation) is needed for confirmation, bovine thyroid stimulating hormone is not generally commercially available. 13 Failure to explore the option of treatment when clinical evidence indicates reasonable suspicion of hypothyroidism might limit the options offered to clients. A novel high-sensitivity radioimmunoassay procedure for measurement of total thyroxine concentration in psittacine birds and snakes was recently reported. It is hoped that the next phase of this study will include provocative testing of suspect birds if TSH can be obtained.
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