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General Pathology

Rickettsial Diseases

Epidemic Typhus

An acute, severe, febrile, louse-borne disease caused by Rickettsia prowazekii, characterized by prolonged high fever, intractable headache, and a maculopapular rash.

Symptoms, Signs, and Prognosis

After an incubation period of 7 to 14 days, fever, headache, and prostration suddenly occur. Temperature reaches 40° C (104° F) in several days and remains high, with slight morning remission, for about 2 wk. Headache is generalized and intense. Small pink macules appear on the 4th to 6th day, usually in the axillae and on the upper trunk; they rapidly cover the body, generally excluding the face, soles, and palms. Later the rash becomes dark and maculopapular; in severe cases, the rash becomes petechial and hemorrhagic. Splenomegaly occurs in some cases. Hypotension occurs in most seriously ill patients; vascular collapse, renal insufficiency, encephalitic signs, ecchymosis with gangrene, and pneumonia are poor prognostic signs. Fatalities are rare in children < 10 yr, but mortality increases with age and may reach 60% in untreated persons > 50 yr.

Adrenocortical Hyperfunction (Hyperadrenalism)

Hypercortisolism (Cushing Syndrome) is caused by any condition that produces an elevation in glucocorticoid levels. The causes of this syndrome are 
A. Exogenous through administration of exogenous glucocorticoids; the most common causeB. Endogenous 
1. Hypothalamic-pituitary diseases causing hypersecretion of ACTH (Cushing disease)
2. Adrenocortical hyperplasia or neoplasia 
3. Ectopic ACTH secretion by nonendocrine neoplasms (paraneoplastic)


Pathological features 

- The main lesions of Cushing syndrome are found in the pituitary and adrenal glands. 
- The most common change in the pituitary, results from high levels of endogenous or exogenous  glucocorticoids, is termed Crooke hyaline change. In this condition, the normal granular, basophilic cytoplasm of the ACTH-producing cells in the anterior pituitary is replaced by homogeneous, lightly basophilic material. This is due to accumulation of intermediate keratin filaments in the cytoplasm. 
- There is one of four changes in the adrenal glands, which depends on the cause.
1. Cortical atrophy 
2. Diffuse hyperplasia
3. Nodular hyperplasia 
4. Adenoma, rarely a carcinoma 

1. In patients in whom the syndrome results from exogenous glucocorticoids, suppression of endogenous ACTH results in bilateral cortical atrophy, due to a lack of stimulation of the cortex by ACTH. In cases of endogenous hypercortisolism, in contrast, the adrenals either are hyperplastic or contain a cortical neoplasm. 
2. In Diffuse hyperplasia the adrenal cortex is diffusely thickened and yellow, as a result of an increase in the size and number of lipid-rich cells in the zonae fasciculata and reticularis. 
3. Nodular hyperplasia, which takes the form of bilateral, up to 2.0-cm, yellow nodules scattered throughout the cortex. 

4. Primary adrenocortical neoplasms causing Cushing syndrome may be benign or malignant. The  adrenocortical adenomas are yellow tumors surrounded by capsules, and most weigh < 30 gm .

Chronic lymphocytic leukaemia

Commoner in middle age. It starts insidiously and often runs a long chronic course

Features:

- Lymphnode enlargement.
- Anaemia (with haemolytic element).
- Moderate splenomegaly.
- Haemorrhagic tendency in late stages.
- Infection.

Blood picture:

- Anaemia with features of haemolytic anaemia
- Total leucocytic count of 50-100,OOO/cu.mm.
- Upto 90-95% cells are lymphocytes and prolymphocytes.
- Thrombocytopenia may be seen.

Bone marrow.  Lymphocytic series cells-are seen. Cells of other series are reduced,
 

Connective tissue diseases
Marfan’s syndrome

a. Genetic transmission: autosomal dominant.
b. Characterized by a defective microfibril glycoprotein, fibrillin.
c. Clinical findings include tall stature, joints that can be hyperextended, and cardiovascular defects, including mitral valve prolapse and dilation of the ascending aorta.

Ehlers-Danlos syndrome
a. Genetic transmission: autosomal dominant or recessive.
b. This group of diseases is characterized by defects in collagen.
c. Clinical findings include hypermobile joints and highly stretchable skin. The skin also bruises easily. Oral findings include Gorlin’s sign and possible temporomandibular joint (TMJ) subluxation. 
The oral mucosa may also appear more fragile and vulnerable to trauma. 

1. Human papillomavirus types 6 and 11 → condyloma acuminta (venereal warts).
2. Molluscum contagiosum is characterized by a bowl shaped lesion filled with keratin, the latter containing the viral inclusions (molluscum bodies) in the squamous cells. 

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. 

Lymphopenia:
Causes

-As part of pancytopenia.
-Steroid administration.

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