Cutaneous Mucinoses
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Direct answer
Cutaneous mucinoses are disorders in which excess glycosaminoglycan-rich mucin accumulates in the dermis, with examples including scleromyxedema, scleredema, pretibial myxoedema and follicular mucinosis. Scleromyxedema causes generalised waxy papules and sclerodermoid thickening, usually with an IgG lambda paraprotein, while scleredema causes non-pitting woody induration of the upper back and neck. Pretibial myxoedema is a localised thickening over the shins that is linked to Graves disease.
What you must remember
- Mucin: glycosaminoglycans, mainly hyaluronic acid and dermatan sulphate, accumulate in the dermis.
- Scleromyxedema: generalised papules and sclerodermoid thickening, with IgG lambda paraproteinaemia.
- Scleredema: non-pitting woody induration of the upper back and neck, often after streptococcal infection or with diabetes.
- Hand sparing: scleredema characteristically spares the hands, which helps separate it from scleromyxedema.
- Pretibial myxoedema: localised, orange-peel thickening over the shins, linked to Graves disease.
- Follicular mucinosis: follicular papules and patchy alopecia on the scalp and face, associated with mycosis fungoides and lymphoma.
- Diagnosis: a biopsy stained with alcian blue at acid pH or colloidal iron highlights dermal mucin.
- Work-up: serum electrophoresis in scleromyxedema, thyroid function in pretibial myxoedema, and glucose and streptococcal history in scleredema.
Sorting mucinoses by distribution and association
Mucinoses are sorted by distribution and by the systemic disease that accompanies them, which is the key discriminator in exams. The table gives the pattern for each entry.
| Disorder | Typical distribution | Key association | Key feature |
|---|---|---|---|
| Scleromyxedema | Generalised, face and hands | IgG lambda paraproteinaemia | Waxy, sclerodermoid papules |
| Scleredema | Upper back and neck | Diabetes, preceding infection | Non-pitting woody induration |
| Pretibial myxoedema | Shins | Graves disease | Orange-peel nodular surface |
| Follicular mucinosis | Scalp and face | Mycosis fungoides, lymphoma | Follicular papules, patchy alopecia |
Each entry carries a systemic association that must be checked, so the table doubles as a work-up list. Learn each row as a pair of distribution and association, since the pattern alone rarely settles the diagnosis. This pairing is what viva examiners usually ask for.
Scleredema is the one that spares the hands, which often separates it from scleromyxedema at the bedside. Histology is confirmatory, and alcian blue or colloidal iron reveal dermal mucin that routine staining may underplay.
Where candidates lose marks
Trap questions in this group mostly test whether candidates look past the skin to the associated disease.
- Trap: diagnosing scleredema in a patient whose thickening spreads to the hands Correct: hand involvement points to scleromyxedema or systemic sclerosis, since scleredema characteristically spares the hands.
- Trap: treating pretibial myxoedema as a purely dermatological problem Correct: it is linked to Graves disease, so thyroid status and eye disease need evaluation.
- Trap: assuming scleromyxedema is a benign skin condition Correct: its paraproteinaemia needs serum electrophoresis and follow-up for associated haematological disease.
Frequently asked questions
Which paraprotein is linked to scleromyxedema?
Scleromyxedema is linked to an IgG lambda monoclonal gammopathy, which is why serum protein electrophoresis forms part of the work-up. Identifying the paraprotein guides follow-up for associated haematological disease.
How does scleredema differ from systemic sclerosis?
Scleredema causes non-pitting woody thickening of the upper back and neck, often after infection or in diabetes, and it characteristically spares the hands. Systemic sclerosis produces tight skin with sclerodactyly, Raynaud phenomenon and internal organ involvement.
Why is pretibial myxoedema important in a dermatology exam?
Pretibial myxoedema is a localised mucinosis over the shins with an orange-peel surface, and it is linked to Graves disease. Its presence should prompt thyroid function testing and examination for thyroid eye disease.
Which stain highlights mucin in cutaneous mucinoses?
Alcian blue at acid pH and colloidal iron stain dermal mucin in biopsies and confirm the diagnosis. Haematoxylin and eosin alone may underplay the mucin, so a special stain is often needed.
What is follicular mucinosis associated with?
Follicular mucinosis is associated with mycosis fungoides and other lymphomas, and it presents with follicular papules and patchy scalp or facial alopecia. It is therefore a sign that prompts a search for underlying lymphoma.