Deep neck infections (DNIs) is a rare manifestation of KD, which include retropharyngeal, parapharyngeal, and peritonsillar abscess. A Population-Based Study among children aged < 12 years showed that of 20,787 patients with Kawasaki disease in the US, 0.6% (130 cases) had DNIs. DNIs often have a rapid onset and can progress to life-threatening complications, such as airway obstruction, jugular vein thrombosis, mediastinal involvement, pericarditis, pneumonia, and arterial erosion. Therefore, timely diagnosis and treatment are necessary. The otolaryngologist may be the initial physician to evaluate a KD patient with parapharyngeal or retropharyngeal space abscess due to its many head and neck manifestations. Although some typical clinical manifestations of KD have appeared in those patients, but the treatment also delayed due to the lack of knowledge of KD by otolaryngologists.[5, 6]
Many of the KD patients with retropharyngeal space inflammation have not found abscesses or liquefaction during pharynx by fine-needle aspiration.[6–8] It is suggested that cellulitis rather than abscess occurs in KD patients. Yu et al  retrospectively analyzed 24 cases of KD patients presenting with retropharyngeal abscess-like edema. None of them were able to fulfill the diagnostic criteria for KD on presentation. They presented as fever with a variety of neck complaints such as neck pain, tender neck mass, torticollis, and limited in range of neck motions. All of those patients were initially managed with empirical antibiotics but were all unresponsive to treatment. As clinical course progressed, more KD signs evolved and fulfilled the complete KD or incomplete KD criteria. One case eventually underwent fine-needle aspiration of the suspicious abscess, subsequent bacterial culture of the aspirated content was negative. After initiation of IVIG, all 24 cases eventually responded satisfactorily to IVIG, this further reinforced the correct diagnosis of KD especially in those cases with incomplete presentation.
However, the causal relationship between the retropharyngeal space inflammation and KD is still difficult to distinguish. Some researchers consider that the retropharyngeal abnormalities in KD are presumably linked to the vasculitis of microvessels that cause oedema and inflammation, which is a non-infectious inflammatory reaction.[11–13] But some researchers consider that the infection of some bacteria such as staphylococcal and streptococcal toxin as superantigens may be involvement in the pathogenesis of KD. Katano et al reported a 10-year-old girl diagnosed with KD, she was subjected to a lymph node biopsy, focal necrosis with inflammatory cell infiltration, including neutrophils and macrophages, was observed in the marginal zone of the cervical lymph node. Streptococcus spp. genome was detected in DNA and RNA samples from a cervical lymph node biopsy specimen. Okada et al reported a 4-year-old boy first presented a peritonsillar and retropharyngeal abscess-like lesion, Surgical tonsillectomy was performed to avoid a risk of mediastinal abscess, but he fulfilled the diagnostic criteria of KD after the operation. Histopathology revealed small lymphatic follicles and neutrophil infiltration in the peritonsillar muscle layer, Streptococcus α-haemolyticus were isolated from both throat and aspiration cultures. Choi et al reported a 3-year-old boy with KD with a coexistent parapharyngeal abscess, After treatment with IVIG (2 g/kg/day) and aspirin (80 mg/kg/day), KD symptoms subsided within 24 hours of IVIG infusion, but the painful left neck swelling persisted and severe torticollis developed. He was treated with ceftriaxone, however, there was no improvement of the left cervical lymphadenitis. The neck CT showed a low density lesion with an irregular thick wall in the left lateral node, suggesting an abscess. After incision and drainage of the parapharyngeal abscess, the cervical adenopathy decreased in size and his torticollis began to resolve. A culture of the abscess revealed the growth of Staphylococcus aureus.
CT scan was helpful in terms of differentiating deep neck abscesses from cellulitis. Holt et al defined the characteristics of a deep neck abscess as a cystic appearance, low-density CT number, air or fluid at the center of the suspected area, and "rim enhancement". In KD patients, the extent of retropharyngeal phlegmon was typically long-segment with no definite "rim enhancement" collections on CT. [9, 10] So the inflammation of the retropharyngeal space caused by KD is often manifested as low-density lesions in the retropharyngeal space on CT. In this condition, early suspicion of KD and subsequent satisfactory response to IVIG may avoid the need for antibiotic treatment or invasive procedures such fine needle aspiration or surgical explorations. However, if neck CT showed a retropharyngeal space abscess, it often indicates that there may be a purulent bacterial infection and may be involved in the onset of KD. Our case is similar to the case reported by Choi et al, the neck CT showed tissues "rim enhancement" which suggesting an abscess. The difference is that our case after treatment with IVIG and aspirin, his neck pain and abscess subsided and no need for incision and drainage. The common offending pathogens of retropharyngeal abscess include Streptococcus, Staphylococcus aureus and epidermidis, with other gram-positive bacteria and anaerobes also seen. Generally, it is not recommended to continue treatment with antibiotics after diagnosis in children with KD, which may aggravate the systemic vascular inflammation. But in our opinion, it is reasonable to managed with empirical antibiotics for KD patient with a retropharyngeal space abscess as the main manifestation.
In summary, we should be alert to the patients with DNIs that show a poor response to initial intravenous antibiotics, as it could be early presentations of KD. KD with deep neck abscess is not an indication for surgery, timely initiation of Kawasaki disease treatment is the key.