You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is A Bone marrow transplant recipient patientdeveloped chest infection. On HRCT 'Tree in bud appearance' is seen. Most likely causative agent is: and explain in detail?
Pneumocystis [Ref: Harrison I7/e p843; Aicle 'Tree in bud sign' in Journal 'Radiology' and 'Radiographics7 Tree-in-bud is a sign seen in HRCT, most commonly seen with endobronchial spread of Tuberculosis, but can be seen with a wide variety of conditions, most commonly infections. (Described ahead in detail). Theoretically all the options can cause 'Tree-in-bud' sign (although Klebsiella has not been mentioned in the list). So the next clue is Bone marrow transplant. Bone marrow transplant causes a transient state of immunological deficiency leading to a wide variety of oppounistic infections. Among the given options, according to the table and text of Harrison (17/e chapter 'Infections in Transplant Recipients') Pneumocystis and RSV can cause pneumonia after transplant: butPneumocystis is a much more common than RSV. Common Sources of Infections after Hematopoietic Stein Cell Transplantation Period after Transplantation Infection Site Early (<1 Month) Middle (1-4 months) Late (>6 Months) Disseminated Aerobic gram-negative, grain-positive bacteria Nocardia Candida, Aspergillus Encapsulated bacteria (Streptococcus pneumoniae, Haemophilus influenzae, Neisseria meningitidis) Skin and mucous membranes HSV- HHV-6 VZV Lungs Candida, Aspergillus HSV CMV, seasonal respiratory viruses Pneumocystis Toxoplasma Pneumocystis Gastrointestinal tract CMV Kidney BK virus, adenovirus BK virus Brain HHV-6 Toxoplasma Toxoplasma JC virus Bone marrow HHV-6 Tree-in-bud sign The tree-in-bud sign is a finding seen on thin-section computed tomographic images of the lung (HRCT). (Not seen on X-rays) Peripheral, small, centrilobular nodules are connected to linear, branching opacities that have more than one contiguous branching site, thus resembling a budding or, fruiting tree: this is known as tree-in-bud-pattern. It represents dilated and impacted (mucus or pus-filled) centrilobular bronchioles. The presence of tree-in-bud is indicative of small airway disease. It is most commonly associated with endobronchial spread of Mycobacterium tuberculosis. But it can also be seen in a large number of conditions. Pulmonary infectious disorders involving the small airways are the most common causes of the tree-in-bud sign. Any infectious organism, including bacterial, mycobacterial, viral, parasitic, and fungal agents, can involve the small airways and cause a tree-in-bud pattern. Causes of Tree-in-bud appearance Peripheral airway disease Infection Bacterial Mycobacterium tuberculosis M avium-intracellulare complex Staphylococcus aureus Haemophilus influenzae Fungal Aspergillus Pneumocystis carinii, (renamed Pneumocystis jiroveci) Viral Cytomegalovirus Respiratory syncytial virus Congenital disorders Cystic fibrosis Kaagener syndrome Idiopathic disorders Obliterative bronchiolitis Diffuse panbronchiolitis A spiration Inhalation Toxic fumes and gases Immunologic disorders Allergic bronchopulmonary aspergillosis Connective tissue disorders Rheumatoid ahritis Sjo-gren syndrome Peripheral pulmonary vascular disease Neoplasms Primary pulmonary lymphoma Neoplastic pulmonary emboli Gastric cancer Breast cancer Ewing sarcoma Renal cancer