Herpes simplex is subdivided into type 1 and 2, the former usually developing lesions around the lips and mouth and the latter producing vesicular lesions in the genital region 
 - contracted by physical contact; incubation 2-10 days.
 - primary HSV I usually is accompanied by systemic signs of fever and Lymphadenopathy, while recurrent herpes is not associate with systemic signs.
 - dentists often become infected by contact with patient saliva and often develop extremely painful infections on the fingers (herpetic whitlow).
 - Herpes viruses remain dormant in sensory ganglia and are reactivated by stress, sunlight, menses, etc. 

 - Herpes gingivostomatitis is MC primary HSV 1 infectionÆpainful, vesicular eruptions that may extend for the tongue to the retropharynx.
 - Herpes keratoconjunctivitis (HSV 1)
 - Kaposi's varicelliform eruption refers to an HSV 1 infection superimposed on a previous dermatitis, usually in an immunodeficient person.
 - laboratory: culture; ELISA test on vesicle fluid; intranuclear inclusions within multinucleated squamous cells in scrapings (Tzanck preps) of vesicular lesions. 

Osteogenesis Imperfecta (OI) (Brittle bone diseases) 

It is a group of hereditary disorders caused by gene mutations that eventuate in defective synthesis of and thus premature degradation of type I collagen. The fundamental abnormality in all forms of OI is too little bone, resulting in extreme susceptibility to fractures. The bones show marked cortical thinning and attenuation of trabeculae. 

Extraskeletal manifestations also occur because type I collagen is a major component of extracellular matrix in other parts of the body. The classic finding of blue sclerae  is attributable to decreased scleral collagen content; this causes a relative transparency that allows the underlying choroid to be seen. Hearing loss can be related to conduction defects in the middle and inner ear bones, and small misshapen teeth are a result of dentin deficiency 

Megaloblastic anaemia

Metabolism: B12(cyanocobalamin) is a coenzyme in DNA synthesis and for maintenance of nervous system. Daily requirement 2 micro grams. Absorption in terminal ileum in the presence gastric intrinsic factor. It is stored in liver mainly-

Folic acid (Pteroylglutamic acid) is needed for DNA synthesis.. Daily requirement 100 micro grams. Absorption in duodenum  and jejunum

Causes of deficiency .-

- Nutritional deficiency-
- Malabsorption syndrome.
- Pernicious anaemia (B12).
- Gastrectomy (B12).
- Fish tapeworm infestation (B12).
- Pregnancy and puerperium (Folic acid mainly).
- Myeloproliferative disorders (Folic acid).
- Malignancies (Folic acid).
- Drug induced (Folic-acid)

Features:

(i) Megaloblastic anaemia.
(ii) Glossitis.
(iii) Subacute combined degeneration (in B12deficiency).

Blood picture :

- Macrocytic normochromic anaemia.
- Anisocytosis and poikilocytosis with Howell-Jolly bodies and  basophilic stippling.
- Occasional megalo blasts may be-seen.
- Neutropenia with hypersegmented neutrophills and macropolycytes.
- Thrombocytopenia.
- Increased MVC and MCH with normal or decreased MCHC.

Bone marrow:

- Megaloblasts are seen. They are larger with a more open stippled chromatin. The nuclear maturation lags behind. the cytoplasmic maturation. Maturation arrest is seen (more of early forms).
- Immature cells of granulocyte series are also larger.
 -Giant stab forms (giant metamyelocytes).
 

Pheochromocytoma

Pheochromocytomas are neoplasms composed of chromaffin cells, which as their normal counterparts synthesize and release catecholamines. 

1. Arise in association with one of several familial syndromes such as MEN syndromes, type 1 neurofibromatosis, von Hippel-Lindau disease, and Sturge-Weber syndrome. 
2. Are extra-adrenal, occurring in sites such as the organ of Zuckerkandl and the carotid body, where they are usually called paragangliomas rather than pheochromocytomas. 
3. Are bilateral; but in association with familial syndromes, this figure may rise to 50%. 
4. Are malignant; frank malignancy, however, is more common in extra-adrenal tumors.  

Gross features

- The size of these tumors is quite variable ranging from small to huge masses. 
- Sectioning shows yellow-tan, well-defined tumor that compress the adjacent adrenal. Large lesions display areas of hemorrhage, necrosis, and cystic degeneration.  
- Incubation of the fresh tissue with potassium dichromate solutions converts the tumor a dark brown color.

Microscopic features
- These tumors are composed of polygonal to spindle-shaped chromaffin cells and their supporting sustentacular cells, arranged in well-defined small nests (Zellballen)," rimmed by a rich vascular network.
- The cytoplasm is often finely granular (catecholamine-containing granules) 
- The nuclei are often quite pleomorphic. 
- Both capsular and vascular invasion may be encountered in benign lesions, and the presence of mitotic figures per se does not imply malignancy. Therefore, the definitive diagnosis of malignancy in pheochromocytomas is based exclusively on the presence of metastases. These may involve regional lymph nodes as well as more distant sites, including liver, lung, and bone. 

The laboratory diagnosis of pheochromocytoma is based on demonstration of increased urinary excretion of free catecholamines and their metabolites, such as vanillylmandelic acid (VMA)&  metanephrines.

Achrondroplasia 
is a major cause of dwarfism. The underlying etiology is a point mutation in the fibroblast growth factor receptor, which causes inhibition of chondrocyte proliferation, which is associated with suppression of the normal epiphyseal growth plate expansion. Thus, long bone growth is markedly shortened.
The most conspicuous changes include disproportionate shortening of the proximal extremities, bowing of the legs, and a lordotic posture. 

Microscopically, the cartilage growth plates are disorganized and hypoplastic. 

Acute leukaemia
Lympheblastic is commoner in children and myeloblastic in adults .

Features:
- Anaemia.
- Fever and infections especially oral and respiratory.
- Haemorrhagic tendencies.
- Bone pains and tenderness (sternal).
- Lymphnode enlargement especially in lymphocytic.
- Gum hypertrophy especially in monocytic.

Blood picture:

- Anaemia and thrombocytopenia.
- Leucocyte count usually 20,-50,000/cu.mm. It may be less in subleukaemic leukaemia (even leucopenic levels may be seen).
- Blast cells form 30-90% of cells. Smudge cells and basket cells are seen .The type of balst cell may be recognised  by the associated more mature forms or by special cytochemical stains
- Blasts may be few in peripheral blood in the aleukamic stage

 Bone Marrow

- May be a dry tap , necessitating a trephine biopsy 
- Hypercellular with 70-90% blasts
- Reduction in megakaryocytes and erythroid cells