Collections of cells in the epidermis

Collections of cells in the Epidermis             See DX Path for details of the conditions below

They can be neutrophils, eosinophils, lymphocytes, melanocytes or histiocytes plus Paget cells. They all form collections within the epidermis and clinically appear as pustules or they induce scale. So the red scaly mnemonic PMs PETAL  or the Pustule mnemonic II should pick them up.

Neutrophils in the epidermis can be seen in a variety of inflammatory conditions but remember Acne and folliculitis, Gonococcemia, Necrolytic migratory erythema, Pemphigus erythematosus or foliaceous, Neonatal pustular melanosis, Scabies and Halogenodermas.


If you see Pustules in the epidermis the mnemonic is II

I - Infective  Viral, Bacterial, Fungal, Rickettsial, Protozoa
I Inflammatory eg Drugs, Pustular psoriasis, Rare ( Scabies, Necrolytic migratory erythema, Subcorneal pustular dermatosis, Neonatal pustular melanosis, Erosive pustular dermatosis, Acrodermatitis enteropathica, Halogenodermas)

Eosinophils in the Epidermis

This is known as eosinophilic spongiosis  and is commonly seen in Pemphigoid and Pemphigus, Acute Contact Dermatitis, Arthropod bites, Eosinophilic pustular Folliculitis, Incontinentia pigmenti and Erythema toxicum Neonatorum
Still remember the Pustular Mnemonic II Infective and Inflammatory. Most of the eosinophilic pustules come under the inflammatory list of diseases.

Eosinophilic spongiosis

Lymphocytes in the Epidermis

These can be small normal looking lymphocytes in PMLE, Acute dermatitis, Pityriasis rosea, Pityriasis lichenoides, Graft versus host disease and Erythema multiforme and collections of atypical lymphocytes (Pautrier microabscesses) in Mycosis fungoides. They tend not to form pustules but either cause keratinocyte necrosis, or spongiosis or irritate the keratinocytes causing scale so most are caught by the red scaly mnemonic PMs PETAL

Pityriasis lichenoides acuta

Melanocytes in the Epidermis

Melanocytes in the Epidermis can be as single cells in Superficial spreading melanoma  showing Pagetoid spread or as nests as in Spitz and Reed nevi or as single cells in neonatal congenital nevi, recurrent nevi and acral nevi.

Superficial spreading melanoma

Histiocytes in the Epidermis

These are really Langerhans cells. They occur in nests and cause a red scaly rash.

Langerhans cell histiocytosis

Epidermal invasion by other cells

Pagetoid spread of cells or nests in the Epidermis.

Pagetoid spread is the upward movement of atypical melanocytes into the upper spinous or sub granular layers of the epidermis and is seen in melanoma. However it is also seen in the centre of Spitz nevi, in Reed or spindled cell nevi and in some acral nevi where the lesions are benign. Some nevi of special sites will also show this phenomenon. Usually though these are single cells rather than nests but Spitz nevi do have nests high up in the epidermis.

Other tumours showing Pagetoid  spread.

Paget's disease of the nipple
Extramammary Pagets
Bowen's disease
Intra epidermal sebaceous carcinoma
Intraepidermal Merkel cell carcinoma

Extramammary Paget's disease

Rarely T cell lymphoma and histiocytosis will show pale cells in the epidermis in nests

To separate out these conditions you need to undertake immunofluorescence studies with specific cell marker antibodies.

Last thing to mention is the Borst- Jadassohn phenomenon

These are usually discrete clones of pale keratinocytes in the epidermis in irritated seborrheoic keratosis. However they can be malignant keratinocytes in Bowen's disease and rarely can also be seen in hidroacanthoma simplex, a form of eccrine poroma confined to the epidermis.

Clonal seborrhoeic keratosis