Presentation
In individuals with tuberous sclerosis, KTs commonly present with multiple firm red-colored to skin-colored nodules or tumors that emanate from the proximal nail fold or, less often, proximal skin beneath the nail. They often develop after puberty; increase in number over time; more frequently occur in the toenails than fingernails (the most common sites are on the big toe and thumb); are generally 5 to 10 mm in length but occasionally grow to far larger sizes; and may be or become disfiguring, painful, and/or incapacitating. Nearly 50% of post-puberty individuals with tuberous sclerosis have KTs. (Tuberous sclerosis is also associated with a second type of angiofibroma, adenoma sebaceum, also termed facial angiofibroma, in ~75% of cases.) Individuals presenting with KTs that do not have tuberous sclerosis commonly present with a single lesion in a nail bed. KT may also present as a recurrence of a lesion at the site where it was surgically removed. Rare cases of KTs have had a history of crushing trauma at the sites where the KTs later developed. Pathology
Microscopic histopathological analyses of KTs commonly reveal a lesion with epidermal acanthosis (i.e. thickening of the skin), hyperkeratosis (i.e. thickening of the outermost layer of the epidermis), and skin features typical of angiofibroma viz., spindle-shaped or star-shaped fibroblasts and ectatic blood vessels in a dense collagen fiber connective tissue background. Etiology
In cases associated with tuberous sclerosis, KTs appear to be a result of this diseases associated genetic abnormalies, i.e.
Acetylcholine then binds to M2 muscarinic receptors, causing the decrease in heart rate that is referred to as reflex bradycardia.The M2 muscarinic receptors decrease the heart rate by inhibiting depolarization of the sinoatrial node via Gi protein-coupled receptors and through modulation of muscarinic potassium channels. Additionally, M2 receptors reduce the contractile forces of the atrial cardiac muscle and reduce the conduction velocity of the atrioventricular node (AV node). However, M2 receptors have no effect on the contractile forces of the ventricular muscle.Stimuli causing reflex bradycardia include:

Oculocardiac reflex
Sympathetic response to intracranial hypertension
Systemically administered norepinephrine (α-adrenergic effects on systemic vasculature exceed the effects of β1-adrenergic effects on the heart)


== References ==