NEET MDS Lessons
General Pathology
Posterior Pituitary Syndromes
The posterior pituitary, or neurohypophysis, is composed of modified glial cells (termed pituicytes) and axonal processes extending from nerve cell bodies in the hypothalamus. The hypothalamic neurons produce two peptides: antidiuretic hormone (ADH) and oxytocin that are stored in axon terminals in the neurohypophysis.
The clinically important posterior pituitary syndromes involve ADH production and include
1. Diabetes insipidus and
2. Inappropriate secretion of high levels of ADH.
- ADH is released into the general circulation in response to increased plasma oncotic pressure & left atrial distention.
- It acts on the renal collecting tubules to increase the resorption of free water.
- ADH deficiency causes diabetes insipidus, a condition characterized by polyuria. If the cause is related to ADH Diabetes insipidus from - - ADH deficiency is designated as central, to differentiate it from nephrogenic diabetes insipidus due to renal tubular unresponsiveness to circulating ADH.
- The clinical manifestations of both diseases are similar and include the excretion of large volumes of dilute urine with low specific gravity. Serum sodium and osmolality are increased as a result of excessive renal loss of free water, resulting in thirst and polydipsia.
- ADH excess causes resorption of excessive amounts of free water, with resultant hyponatremia.
- The most common causes of the syndrome include the secretion of ectopic ADH by malignant neoplasms (particularly small-cell carcinomas of the lung), and local injury to the hypothalamus and/or neurohypophysis.
- The clinical manifestations are dominated by hyponatremia, cerebral edema, and resultant neurologic dysfunction.
Plasma Cell Pathology
A. Multiple myeloma
1. Plasma cell neoplasm that results in the proliferation of monoclonal plasma cells. These tumor cells produce nonfunctional immunoglobulins.
2. Laboratory findings include:
a. Monoclonal IgG spike.
b. Bence-Jones proteins found in urine.
3. Radiographic findings: characteristic “punched-out” radiolucencies in bones.
Lysosomal (lipid) storage diseases
- Genetic transmission: autosomal recessive.
- This group of diseases is characterized by a deficiency of a particular lysosomal enzyme. This results in an accumulation of the metabolite, which would have otherwise been degraded by the presence of normal levels of this specific enzyme.
Diseases include:
Gaucher’s disease
(1) Deficient enzyme: glucocerebrosidase.
(2) Metabolite that accumulates: glucocerebroside.
(3) Important cells affected: macrophages.
Tay-Sachs disease
(1) Deficient enzyme: hexosaminidase A.
(2) Metabolite that accumulates: GM2 ganglioside.
(3) Important cells affected: neurons.
(4) Symptoms include motor and mental deterioration, blindness, and dementia.
(5) Common in the Ashkenazi Jews.
Niemann-Pick disease
(1) Deficient enzyme: sphingomyelinase.
(2) Metabolite that accumulates: sphingomyelin.
(3) Important cells affected: neurons.
Herpes zoster, or shingles
- represents reactivation of a latent varicella-zoster infection.
- virus lies dormant in sensory dorsal root ganglia and when activated involves the distribution (dermatome) of the sensory nerve with a painful vesicular eruption.
- trigeminal verve distribution → Ramsay Hunt syndrome
- may indicate the presence of advanced neoplastic disease or be a complication of chemotherapy.
Cardiac arrhythmia
Cardiac arrhythmia is a group of conditions in which muscle contraction of the heart is irregular for any reason.
Tachycardia :A rhythm of the heart at a rate of more than 100 beats/minute , palpitation present
Causes : stress, caffeine, alcohol, hyperthyroidism or drugs
Bradycardia : slow rhythm of the heart at a rate less than 60 beats/min
Atrial Arrhythmias
- Atrial fibrillation
Atrial Dysrhythmias
- Premature atrial contraction
- Atrial flutter
- Supraventricular tachycardia
- Sick sinus syndrome
Ventricular Arrhythmias
- Ventricular fibrillation
Ventricular Dysrhythmias
- Premature ventricular contraction
- Pulseless electrical activity
- Ventricular tachycardia
- Asystole
Heart Blocks
- First degree heart block
- Second degree heart block
o Type 1 Second degree heart block a.k.a. Mobitz I or Wenckebach
o Type 2 Second degree heart block a.k.a. Mobitz II
- Third degree heart block a.k.a. complete heart block
Atrial fibrillation
Atrial fibrillation is a cardiac arrhythmia (an abnormality of heart rate or rhythm) originating in the atria.
AF is the most common cardiac arrhythmia
Signs and symptoms
Rapid and irregular heart rates
palpitations, exercise intolerance, and occasionally produce angina and congestive symptoms of shortness of breath or edema
Paroxysmal atrial fibrillation is the episodic occurence of the arrhythmia Episodes may occur with sleep or with exercise
Diagnosis:
Electrocardiogram
- absence of P waves
- unorganized electrical activity in their place
- irregularity of R-R interval due to irregular conduction of impulses to the ventricles
Causes:
- Arterial hypertension
- Mitral valve disease (e.g. due to rheumatic heart disease or mitral valve prolapse)
- Heart surgery
- Coronary heart disease
- Excessive alcohol consumption ("binge drinking" or "holiday heart")
- Hyperthyroidism
- Hyperstimulation of the vagus nerve, usually by having large meals
Treatment
Rate control by
Beta blockers (e.g. metoprolol)
Digoxin
Calcium channel blockers (e.g. verapamil)
Rhythm control
Electrical cardioverion by application of a DC electrical shock
Chemical cardioversion is performed with drugs eg amiodarone
Radiofrequency ablation : uses radiofrequency energy to destroy abnormal electrical pathways in heart tissue It is used in recurrent AF
In confirmed AF, anticoagulant treatment is a crucial way to prevent stroke
Atrial flutter
Atrial flutter is a regular, rhythmic tachycardia originating in the atria. The rate in the atria is over 220 beats/minute, and typically about 300 beats/minute
he morphology on the surface EKG is typically a sawtooth pattern.
The ventricles do not beat as fast as the atria in atrial flutter
Supraventricular tachycardia
apid rhythm of the heart in which the origin of the electrical signal is either the atria or the AV node
it is important to determine whether a wide-complex tachycardia is an SVT or a ventricular tachycardia, since they are treated differently
Sick sinus syndrome : a group of abnormal heartbeats (arrhythmias) presumably caused by a malfunction of the sinus node, the heart's "natural" pacemaker.
Ventricular fibrillation
is a cardiac condition which consists of a lack of coordination of the contraction of the muscle tissue of the large chambers of the heart. The ventricular muscle twitches randomly, rather than contracting in unison, and so the ventricles fail to pump blood into the arteries and into systemic circulation.
Ventricular fibrillation is a medical emergency: if the arrhythmia continues for more than a few seconds, blood circulation will cease, as evidenced by lack of pulse, blood pressure and respiration, and death will occur. Ventricular fibrillation is a cause of cardiac arrest and sudden cardiac death
Pleural effusion is a medical condition where fluid accumulates in the pleural cavity which surrounds the lungs, making it hard to breathe.
Four main types of fluids can accumulate in the pleural space:
Serous fluid (hydrothorax)
Blood (hemothorax)
Lipid (chylothorax)
Pus (pyothorax or empyema)
Causes:
Pleural effusion can result from reasons such as:
- Cancer, including lung cancer or breast cancer
- Infection such as pneumonia or tuberculosis
- Autoimmune disease such as lupus erythematosus
- Heart failure
- Bleeding, often due to chest trauma (hemothorax)
- Low oncotic pressure of the blood plasma
- lymphatic obstruction
- Accidental infusion of fluids
Congestive heart failure, bacterial pneumonia and lung cancer constitute the vast majority of causes in the developed countries, although tuberculosis is a common cause in the developing world.
Diagnosis:
- Gram stain and culture - identifies bacterial infections
- Cell count and differential - differentiates exudative from transudative effusions
- Cytology - identifies cancer cells, may also identify some infective organisms
- Chemical composition including protein, lactate dehydrogenase, amylase, pH and glucose - differentiates exudative from transudative effusions
- Other tests as suggested by the clinical situation - lipids, fungal culture, viral culture, specific immunoglobulins
Keratoses (Horny Growth)
1. Seborrheic keratosis is a common benign epidermal tumor composed of basaloid (basal cell-like) cells with increased pigmentation that produce a raised, pigmented, "stuck-on" appearance on the skin of middle-aged individuals.
- they can easily be scraped from the skin's surface.
- frequently enlarge of multiply following hormonal therapy.
- sudden appearance of large numbers of Seborrheic keratosis is a possible indication of a malignancy of the gastrointestinal tract (Leser-Trelat sign).
2. An actinic keratosis is a pre-malignant skin lesion induced by ultraviolet light damage.
- sun exposed areas.
- parakeratosis and atypia (dysplasia) of the keratinocytes.
- solar damage to underlying elastic and collagen tissue (solar elastosis).
- may progress to squamous carcinoma in situ (Bowen's disease) or invasive cancer.
3. A keratoacanthoma is characterized by the rapid growth of a crateriform lesion in 3 to 6
weeks usually on the face or upper extremity.
- it eventually regresses and involutes with scarring.
- commonly confused with a well-differentiated squamous cell carcinoma.