NEOPLASIA

 An abnormal. growth, in excess of and uncoordinated with normal tissues Which persists in the same excessive manner after cessation of the stimuli which evoked the change.

Tumours are broadly divided by their behaviors into 2 main groups, benign and malignant.

Through most tumours can be classified in the benign or malignant category . Some exhibits an intermediate behaviours.

CLASSIFICATION

Some tumours can not be clearly categorized in the above table e.g.

• Mixed tumours like fibroadenoma of the breast which is a neoplastic proliferation of both epithelial and mesenchmal tissues.
• Teratomas which are tumours from germ cells (in the glands) and totipotent cells

(in extra gonodal sites like mediastinun, retroperitoneum and presacral region). These are composed of multiple tissues indicative of differentiation into the derivatives of the three germinal layers.

• Hamartomas which are malformations consisting of a haphazard mass of  tissue normally present at that site.

N. meningiditis

Major cause of fulminant bacteremia and meningitis.  Has a unique polysaccharide capsule.  It is spread person to person by the respiratory route.  Frequently carried in nasopharynx, and carriage rates increased by close quarters.  Special risk in closed populations (college dorms) and in people lacking complement.  Sub-saharan Africa has a “meningitis belt.”

Pathogenesis is caused by adherence factors that attach to non-ciliated nasopharyngeal epithelium. These factors include pili which promote the intial epithelial (and erythrocyte) attachment, and Opa/Opc surface binding proteins.

Adherence stimulates engulfment of bacteria by epithelial cells.  Transported to basolateral surface.

The polysaccharide capsule is a major virulence factor that prevents phagocytosis and lysis. 

A lipo-oligosaccharide endotoxin also contributes to sepsis.

Acanthosis nigricans is a pigmented skin lesion commonly present in the axilla which is a phenotypic marker for an insulin-receptor abnormality as well as a marker for adenocarcinoma, most commonly of gastric origin.

Hypoparathyroidism

Hypoparathyroidism is a condition of reduced or absent PTH secretion, resulting in hypocalcaemia and hyperphosphataemia. It is far less common than hyperparathyroidism.

The causes of hypoparathyroidism are:
- Removal or damage of the parathyroid glands during thyroidectomy—most common cause of hypoparathyroidism resulting from inadvertent damage or removal.
- Autoimmune parathyroid disease—usually occurs in patients who have another autoimmune endocrine disease, e.g. Addison’s disease (autoimmune endocrine syndrome type 1).
- Congenital deficiency (DiGeorge syndrome)— rare, congenital disorder caused by arrested development of the third and fourth branchial arches, resulting in an almost complete absence of the thymus and parathyroid gland.

The effects of hypoparathyroidism are:
- ↓ release of Ca²⁺ from bones. 
- ↓ Ca²⁺ reabsorption but ↑ PO ₄³⁻ re absorption by the kidneys
- ↓ 1-hydroxylation of 25-hydroxyvitamin D by kidney.

Most symptoms of hypoparathyroidism are those of hypocalcaemia:
- Tetany—muscular spasm provoked by lowered plasma Ca 2+ 
- Convulsions.
- Paraesthesiae.
- Psychiatric disturbances, e.g. depression, confusional state and even psychosis.
- Rarely—cataracts, parkinsonian-like movement disorders, alopecia, brittle nails.

Management is by treatment with large doses of oral vitamin D; the acute phase requires intravenous calcium and calcitriol (1,25-dihydroxycholecalciferol, i.e.  activated vitamin D).