Rhodococcus equi

Important Special Stains #NEETPG TISSUE COMPONENTS 1. PAS : glycogen, basement membrane, fungal walls. 2. PAS + diastase (PAS-D) : the splitter. Glycogen disappears (digested); fungi, α1-antitrypsin globules, Whipple macrophages stay. "Diastase-resistant = not glycogen." 3. Masson trichrome : collagen / fibrosis (blue-green). Your go-to for cirrhosis staging. 4. Reticulin (silver) : reticulin framework - collapse patterns in liver, marrow architecture. 5. Congo red : amyloid >> apple-green birefringence under polarised light (the polarised-light detail is the answer, not congo red alone). 6. Verhoeff-van Gieson : elastic fibres (aorta, Marfan/vasculitis). 7. Mucicarmine : epithelial mucin (adenocarcinoma) + Cryptococcus capsule. 8. Alcian blue : acid mucins. 9. Oil Red O / Sudan : lipid >> needs frozen section (fat washes out in routine processing). MICROBES 10. Ziehl-Neelsen : acid-fast bacilli (TB). 11. Fite : M. leprae + Nocardia (modified, gentler decolourisation - the leprosy-specific answer). 12. Auramine-rhodamine : AFB, fluorescent (screening). 13. GMS (Gomori methenamine silver) : fungi + Pneumocystis jirovecii. 14. Warthin-Starry / silver : spirochetes (syphilis), H. pylori, Bartonella. 15. Giemsa : H. pylori, Leishmania (LD bodies), malaria, mast cells. 16. Gram stain : bacteria. PIGMENTS & DEPOSITS 17. Prussian blue (Perls) : iron / hemosiderin. 18. Von Kossa : calcium salts (phosphate/carbonate) - stains the anion. 19. Alizarin red : calcium ion directly. 20. Fontana-Masson : melanin. 21. Rhodanine / Orcein : copper (Wilson disease). Orcein also marks HBsAg + elastic. NEURO 22. Luxol fast blue : myelin (demyelination). 23. Nissl / cresyl violet : Nissl substance (neuronal loss). 24. Bielschowsky (silver) : plaques + neurofibrillary tangles (Alzheimer).

Important Inclusion Bodies & Eponymous Bodies #NEETPG VIRAL INCLUSIONS 1. Negri bodies : Rabies. Cytoplasmic, eosinophilic. Hippocampus + Purkinje cells. 2. Owl-eye inclusion : CMV. Intranuclear, basophilic, with a halo. 3. Cowdry A : HSV, VZV, CMV. Intranuclear eosinophilic with clear halo. 4. Cowdry B : Polio, adenovirus. 5. Guarnieri bodies : Smallpox / vaccinia. Cytoplasmic. 6. Molluscum (Henderson-Paterson) bodies : Molluscum contagiosum. Cytoplasmic. 7. Torres bodies : Yellow fever. Cytoplasmic. "BODIES" IN NON-VIRAL DISEASE 8. Mallory-Denk bodies : Alcoholic hepatitis. Damaged cytokeratin 8/18. Also NASH, Wilson, Indian childhood cirrhosis. 9. Russell bodies : Plasma cells (Ig accumulation). The cell = Mott cell. 10. Dutcher bodies : Intranuclear Ig - Waldenström / lymphoplasmacytic lymphoma. (Russell = cytoplasmic, Dutcher = nuclear. Classic paired trap.) 11. Michaelis-Gutmann bodies : Malakoplakia. Targetoid, calcified, von Kossa stain positive. 12. Psammoma bodies : Papillary thyroid Ca, meningioma, serous ovarian, mesothelioma. Laminated calcification. 13. Schaumann + asteroid bodies : Sarcoidosis (inside giant cells). 14. Call-Exner bodies : Granulosa cell tumor. 15. Verocay bodies : Schwannoma (Antoni A regions). NEURO "BODIES" 16. Lewy bodies : Parkinson (α-synuclein). 17. Pick bodies : Pick disease / FTD (tau). 18. Hirano bodies : Alzheimer (actin). 19. Lafora bodies : Lafora disease (myoclonic epilepsy, polyglucosan).

Important Chromosomal Translocations #NEETPG t(9;22) BCR-ABL1 : CML (Philadelphia chromosome). Constitutive tyrosine kinase; imatinib target. Also seen in Ph+ ALL (worse prognosis). t(15;17) PML-RARA : APML / AML-M3. Blocks retinoic acid signalling - ATRA breaks the block. t(8;21) RUNX1-RUNX1T1 : AML-M2. Good prognosis. inv(16) / t(16;16) CBFB-MYH11 : abnormal eosinophils. Good prognosis. t(12;21) ETV6-RUNX1 : childhood B-ALL. Commonest in kids, best prognosis. t(9;11) KMT2A/MLL : AML with monocytic differentiation (M5). Poor. t(8;14) c-MYC - IGH : Burkitt lymphoma. MYC drives proliferation - starry-sky, near-100% Ki-67. t(14;18) BCL2 - IGH : Follicular lymphoma. Anti-apoptosis - cells don't proliferate faster, they just refuse to die. t(11;14) Cyclin D1 (CCND1) - IGH : Mantle cell lymphoma. Cyclin D1+ is the diagnostic reflex. t(11;18) API2-MALT1 - MALT lymphoma. The one that predicts no response to H. pylori eradication. t(2;5) NPM-ALK - Anaplastic large cell lymphoma (ALK+, better prognosis). t(11;22) EWSR1-FLI1 : Ewing sarcoma / PNET. MIC2 / CD99 membranous. t(X;18) SS18-SSX : Synovial sarcoma. t(2;13) PAX3-FOXO1 : Alveolar rhabdomyosarcoma. t(12;16) FUS-DDIT3 : Myxoid liposarcoma. t(17;22) COL1A1-PDGFB : Dermatofibrosarcoma protuberans.