Mucinoses encompass a group of diverse skin disorders which can vary from minor cosmetic nuisances to potentially severe conditions involving internal organs. All involve the abnormal accumulation of acid mucopolysaccharide (mucin) either diffusely or locally in the skin or even within the hair follicles.
The mucin is composed of glycosaminoglycans (particularly hyaluronic acid) and is normally produced in small amounts as part of the dermal connective tissue by fibroblasts. Interestingly, mucin plays a vital role in the homeostasis of water and salt in the dermis and can actually absorb one thousand times its own weight of water. Thus, in conditions such as mucinoses where mucin production is increased, there is more water retention so that the dermal connective tissue becomes edematous.
The core reason for this upregulated mucin production is unknown. Despite this, mucinoses can still be categorized as either primary mucinoses, where the main histological occurrence is mucin deposition, or cutaneous disorders, where the mucin deposition only constitutes an additional finding (epiphenomenon).
Identification of the mucinosis involves determining the presence of mucin by particular histological techniques. For example, alcian blue is a positively charged dye which may be used to detect mucin molecules containing anionic negatively charged sites via attractive forces.
Microscopic techniques are required to determine the specific localization of mucin in order to determine the form of mucinoses present, i.e. primary (dermal or follicular) or secondary (epidermal, dermal or follicular).
Examples of generalized (extensive) mucinosis include:
Follicular mucinosis (alopecia mucinosa)
This mucinosis is most common in children and adult males in their thirties or forties. It appears that the adult form tends to induce more lesions and last longer. The symptoms include follicular papules (raised spots) often on the neck, face, and scalp that can be singular or in reddened patches of usually 2-5 cm in diameter. Hair loss is common from the affected follicles. In the early stages, this is reversible and the hair will grow back should the condition clear up. In more severe disease, complete follicular destruction disallows normal hair growth even if the disease is controlled.
Papular mucinosis (lichen myxoedematosus)
Some mucinoses such as this have both a localized and generalized form. In this case, the localized form has a more favorable and manageable course compared to the generalized form, scleromyxoedema, which can involve multiple organs and could even prove fatal. For example, oxygen intake is hampered when the lungs are affected or the brain and nervous periphery are damaged when the nervous system is affected.
Examples of localized mucinosis include:
Connective Tissue Naevi
This mucinosis is usually seen in children. It encompasses disorders in which components of the skin layers develop abnormally – it is thought that there they are attributed to a genetic defect, forming a component of some inherited disorders including tuberous sclerosis. The disorders can occur due to reasons including too much collagen (a collagenoma), elastic tissue (an elastoma), smooth muscle, fat or glycosaminoglycans.
Myxoid or Digital Mucus Cyst
This disorder is most common in those in their sixties. It is characterized by varying sizes of benign fluid-filled mucous or myxoid cysts which are found at the base of the finger nail (or sometimes toenail) or close to it. If the cyst happens to overlie the area where the nail forms then it often causes a groove which extends the length of the nail.
This mucinosis appears to occur due to one of two reasons – abnormal mucin accumulation in the skin or due to osteoarthritis when there is extension of the lining of the finger joint.