NEET MDS Lessons
General Pathology
Fibrous and Fibro-Osseous Tumors
Fibrous tumors of bone are common and comprise several morphological variants.
1. Fibrous Cortical Defect and Nonossifying Fibroma
Fibrous cortical defects occur in 30% to 50% of all children older than 2 years of age; they are probably developmental rather than true neoplasms. The vast majority are smaller than 0.5 cm and arise in the metaphysis of the distal femur or proximal tibia; almost half are bilateral or multiple. They may enlarge in size (5-6 cm) to form nonossifying fibromas. Both lesions present as sharply demarcated radiolucencies surrounded by a thin zone of sclerosis. Microscopically are cellular and composed of benign fibroblasts and macrophages, including multinucleated forms. The fibroblasts classically exhibit a storiform pattern. Fibrous cortical defects are asymptomatic and are usually only detected as incidental radiographic lesions. Most undergo spontaneous differentiation into normal cortical bone. The few that enlarge into nonossifying fibromas can present with pathologic fracture; in such cases biopsy is necessary to rule out other tumors.
2. Fibrous Dysplasia
is a benign mass lesion in which all components of normal bone are present, but they fail to differentiate into mature structures. Fibrous dysplasia occurs as one of three clinical patterns:
A. Involvement of a single bone (monostotic)
B. nvolvement of multiple bones (polyostotic)
C. Polyostotic disease, associated with café au lait skin pigmentations and endocrine abnormalities, especially precocious puberty (Albright syndrome).
Monostotic fibrous dysplasia accounts for 70% of cases. It usually begins in early adolescence, and ceases with epiphyseal closure. It frequently involves ribs, femur, tibia & jawbones. Lesions are asymptomatic and usually discovered incidentally. However, fibrous dysplasia can cause marked enlargement and distortion of bone, so that if the face or skull is involved, disfigurement can occur.
Polyostotic fibrous dysplasia without endocrine dysfunction accounts for the majority of the remaining cases.
It tends to involve the shoulder and pelvic girdles, resulting in severe deformities and spontaneous fractures.
Albright syndrome accounts for 3% of all cases. The bone lesions are often unilateral, and the skin pigmentation is usually limited to the same side of the body. The cutaneous macules are classically large, dark to light brown (café au lait), and irregular.
Gross features
• The lesion is well-circumscribed, intramedullary; large masses expand and distort the bone.
On section it is tan-white and gritty.
Microscopic features
• There are curved trabeculae of woven bone (mimicking Chinese characters), without osteoblastic rimming
• The above are set within fibroblastic proliferation
Individuals with monostotic disease usually have minimal symptoms. By x-ray, lesions exhibit a characteristic ground-glass appearance with well-defined margins. Polyostotic involvement is frequently associated with progressive disease, and more severe skeletal complications (e.g., fractures, long bone deformities, and craniofacial distortion). Rarely, polyostotic disease can transform into osteosarcoma, especially following radiotherapy.
Pathology
The branch of medicine dealing with the essential nature of disease, especially changes in body tissues aorgans that cause or are caused by disease. Pathology is the structural and functional manifestations of disease.
Anatomic pathology the anatomical study of changes in the function, structure, or appearance of organs or tissues,including postmortem examinations and the study of biopsy specimens.
Cellular pathology - Cytopathology is a diagnostic technique that examines cells from various body sites to determine the cause or the nature of disease.
Clinical pathology pathology applied to the solution of clinical problems, especially the use of laboratory
methods inclinical diagnosis.
Comparative pathology that which considers human disease processes in comparison with those of other
animals.
Oral pathology that treating of conditions causing or resulting from morbid anatomic or functional changes in thestructures of the mouth.
Surgical pathology the pathology of disease processes that are surgically accessible for diagnosis or treatment.
Human immunodeficiency virus (HIV)
1. Part of the Retroviridae family (i.e., it is a retrovirus).
2. Basic virion structure
a. The nucleocapsid contains single stranded RNA and three enzymes: reverse transcriptase, integrase, and protease.
b. An exterior consists of two glycoproteins, gp120 and gp41, which are imbedded in the lipid bilayer. This lipid bilayer was obtained from the host cell via budding.
3. Virion characteristics
a. The HIV genome includes:
(1) gag gene—codes for core proteins.
(2) pol gene—codes for its three enzymes.
(3) env gene—codes for its two envelope glycoproteins.
b. HIV enzymes
(1) Reverse transcriptase—reverse transcription of RNA to viral DNA.
(2) Integrase—responsible for integrating viral DNA into host DNA.
(3) Protease—responsible for cleaving precursor proteins.
4. Pathogenicity
a. HIV mainly infects CD4 lymphocytes, or helper T cells. Its envelope protein, gp120, binds specifically with CD4 surface
receptors. After entry, viral RNA is transcribed by reverse transcriptase to viral DNA and integrated into the host DNA. New virions are synthesized and released by lysis of the host cell.
b. The predominant site of HIV replication is lymphoid tissues.
c. Although HIV mainly infects CD4 helper T cells, it can bind to any cell with a CD4 receptor, including macrophages, monocytes, lymph node dendritic cells, and a selected number of nerve cells. Macrophages are the first cells infected by HIV.
5. HIV infection versus acquired immunodeficiency syndrome (AIDS).
a. AIDS describes an HIV-infected person who has one of the following conditions:
(1) A CD4 lymphocyte count of less than 200.
(2) The person is infected with an opportunistic infection or other AIDS-defining illness, including (but not limited to) tuberculosis, recurrent pneumonia infections, or invasive cervical cancer.
b. The cause of death in an AIDS patient is most likely due to an opportunistic infection.
6. Common opportunistic infections associated with AIDS:
a. Pneumonia caused by Pneumocystis jiroveci (carinii).
b. Tuberculosis.
c. Periodontal disease—severe gingivitis, periodontitis, ANUG, necrotizing stomatitis.
d. Candidiasis.
e. Oral hairy leukoplakia (EBV).
f. Kaposi’s sarcoma (HHV-8).
g. Recurrent VZV infections.
h. Condyloma acuminatum or verruca vulgaris (warts, HPV)—less common.
i. CMV infections.
j. Disseminated herpes simplex, herpes zoster.
k. Hodgkin’s, non-Hodgkin’s lymphoma.
7. Laboratory diagnosis of HIV
a. ELISA test—detects HIV antibodies.
False negatives do occur.
b. Western blot—detects HIV proteins.
There is a 99% accuracy rate when both the ELISA test and Western blot are used to diagnose HIV infection.
c. PCR—more sensitive; can amplify and identify the virus at an early stage.
8. Treatment
a. Inhibitors of reverse transcriptase.
(1) Nucleoside analogs
(a) Inhibit viral replication via competitive inhibition.
(b) Examples: zidovudine (AZT), didanosine, lami- vudine, stavudine.
(2) Nonnucleoside inhibitors.
(a) Act by binding directly to reverse transcriptase.
(b) Examples: nevirapine, delavirdine.
b. Protease inhibitor.
c. “Triple cocktail” therapy—often consists of two nucleoside inhibitors and a protease inhibitor.
Seborrheic dermatitis is a scaly dermatitis on the scalp (dandruff) and face.
- due to Pitysporium species
- can be seen in AIDS as an opportunistic infection
Immunoglobulins. (Ig)
These are made up of polypeptide chains. Each molecule is constituted by two heavy and two light chains, linked by disulfide (S-S) bonds. The h~ chains are of 5 types, with corresponding, types or immunoglobulin. IgG (gamma), IgM (mu µ ), IgA(alpha α), IgD(delta ), IgE(epsilon)
Each of these can have light chains of either kappa (k) or lambda type.Each chain has a constant portion (constant for the subtype) land a variable portion (antigen specific).
Enzyme digestion can split the Ig molecule into.2 Fab (antibody binding) fragments and one Fc (crystallisable, complement binding ) fragment.
FUNGAL INFECTION
Mucormycosis (Zygomycosis; Phycomycosis)
Infection with tissue invasion by broad, nonseptate, irregularly shaped hyphae of diverse fungal species, including Rhizopus, Rhizomucor, Absidia, and Basidiobolus.
Infection is most common in immunosuppressed persons, in patients with poorly controlled diabetes, and in patients receiving the iron-chelating drug desferrioxamine.
Symptoms and Signs
Rhinocerebral mucormycosis is the most common form, but primary cutaneous, pulmonary, or GI lesions sometimes develop, and hematogenous dissemination to other sites can occur. Rhinocerebral infections are usually fulminant and frequently fatal. Necrotic lesions usually appear on the nasal mucosa or sometimes the palate.
Group A Streptococcus
- scarlet fever usually begins as a Streptococcal pharyngitis/tonsillitis and then develops an erythematous rash beginning on the trunk and limbs with eventual desquamation.
- rash is due to elaboration of erythrogenic toxin by the organism
- face is usually spared, but, if involved there is a characteristic circumoral pallor and the tongue becomes bright red, thus the term "strawberry tongue".
- post-streptococcal immune complex glomerulonephritis is a possible sequela of scarlet fever.
- Dick test is a skin test that evaluates immunity against scarlet fever; no response indicates immunity (anti-toxin antibodies present); erythema indicates no immunity.
- impetigo due to Streptococcus pyogenes is characterized by honey colored, crusted lesions, while those with a predominantly bullous pattern are primarily due to Staphylococcus aureus.
- cellulitis with lymphangitis ("red streaks") is characteristic of Streptococcus pyogenes.
- hyaluronidase is a spreading factor that favors the spread of infection throughout the subcutaneous tissue unlike Staphylococcus aureus which generates coagulase to keep the pus confined.
- erysipelas refers to a raised, erythematous ("brawny edema"), hot cellulitis, usually on the face that commonly produces septicemia, if left untreated.