Monday, 31 October 2011

Electrosurgical waveforms

Electrosurgery (diathermy) equipment converts domestic alternating current into high-frequency alternating current (of various types) which is converted to heat energy as it passes THROUGH a high-resistance medium such as the skin. Haemostasis can only be achieved satisfactorily if the area being diathermied is relatively dry. Each type of electrosurgical current produces its own wavy pattern of current flow, called the waveform.

Different electrical waveforms produce tissue desiccation/fulguration, coagulation, or cutting. Some machines are designed to produce all effects. There is however some overlap between these effects so that the desiccation waveform (dehydration) can be used, albeit not perfectly, for coagulation and cutting.

Monoterminal procedures (without a dispersive plate) produce desiccation/fulguration. Biterminal procedures produce coagulation with a dispersive plate or bipolar electrode (bipolar forceps, keeps the current flow on the surface travelling from one tine of the forceps to the other) or produce coagulation with cutting or pure cutting without appreciable coagulation effect (electrosection) with a dispersive plate. Pure cutting is useful in diagnostic biopsy avoiding the tissue damage associated with coagulation (after the biopsy is taken, haemostasis can be attained by switching to coagulation). 

In electrofulguration, the needle tip is not in contact with the skin. As the spark jumps between the skin and the needle its energy is spread over a greater area, resulting in more superficial tissue damage (superficial dehydration). Deep penetration does not occur because the charring acts as an insulating barrier.

Thursday, 27 October 2011


What does the development of an exophytic nodule on this naevus in the child patient, that has been present since birth, usually represent? Does the patched-hedgehog signalling pathway malfunction in this regard? What advice would you give the parent?

In this naevus, around puberty there is enlargement of the 
sebaceous glands, which are often located abnormally high in the 
dermis, with an increased number of closely set lobules and 
malformed ducts (A). A variety of appendageal tumours, sometimes
multiple, may develop within sebaceous naevi. The most commonly 
reported are trichoblastoma and syringocystadenoma papilliferum
(B). It should be noted that basaloid proliferations (arrow
that are seen in as many as half of all cases of naevus sebaceous
are not always easily differentiated from basal cell carcinoma
(BCC). Misinterpretation of trichoblastoma and basaloid
 proliferation as BCC has caused problems in the past.

How to differentiate between BCC and trichoblastoma 

Short and long answers are provided below as comments.

Tuesday, 25 October 2011


Non-Langerhans cell histiocytosis represents a broad group of different disorders characterized by the proliferation of histiocytes other than Langerhans cells. One of which, is multicentric reticulohistiocytosis shown here in this middle-aged woman with yellow-pink papules and nodules (with scleral involvement). Multicentric reticulohistiocytosis has subtype (multiple reticulohistiocytomas) that is restricted to skin. It is possible that the diffuse, purely cutaneous form is an early stage of multicentric reticulohistiocytosis before the appearance of joint and other lesions. In multicentric reticulohistiocytosis the onset of arthropathy, may precede, follow, or accompany the onset of skin lesions. No treatment is of consistent value for this disease.

The characteristic pathological picture in multicentric reticulohistiocytosis is of infiltration by mononucleated and multinucleated giant cells with voluminous eosinophilic ground-glass cytoplasm (finely granular). In early lesions, the predominant infiltrating cells are histiocytes, lymphocytes and eosinophils, with few giant cells, but the giant cell infiltrate quickly follows.
The multinucleate giant cells (the hallmark of the disease) have 3-10 or more nuclei, which may be placed haphazardly, or along the periphery, or clustered in the centre of the giant cell. They contain variable amounts of lipid and free or esterified cholesterol.

Severe involvement of the face may lead to a leonine facies. Does this disease show Köbner (Koebner) response? What are the diseases that may lead to a leonine facies?

Sunday, 23 October 2011



This young adult presented with these scaly lesions (A). On Wood’s light examination (B), these lesions showed yellow fluorescence, and unsuspected similar lesions more widely scattered were revealed as well. What is the fluorescent substance? Is it water-soluble?

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June 2014

Thursday, 20 October 2011

Cryotherapy of a cherry angioma

Cherry angiomas (Campbell de Morgan spots) occur predominantly on the trunk and proximal parts of the limbs. Cryotherapy option, when treatment is required, works but it is a less-well controlled method than others.  

The freeze time BEGINS at the moment the target area of skin is COMPLETELY frozen (the ice ball). Liquid nitrogen is then sprayed intermittently on the target area to maintain the ice ball at the required margin. Liquid nitrogen spray is halted when the freeze time is up.

In cherry angiomas: Freeze time --> 10 seconds, lesions in general often need more than one freeze. Margin of normal skin also frozen (mm): 1

In larger lesions, the liquid nitrogen spray is directed from the side of the lesion
. This allows the extraneous liquid nitrogen to ricochet from the surface of the lesion into the air rather than over normal surrounding skin. If the larger lesion is sprayed directly from the top the extraneous liquid nitrogen will travel across the normal surrounding skin and invariably the physician will terminate cryosurgery before the central base of the lesion has been sufficiently frozen. 

The extent of injury is determined by the rate of freezing, the coldest temperature reached, the freeze time and the rate of thawing. Pain peaks during thawing. Use words like discomfort, burn, or pain whenever appropriate when describing the reaction so that the patient will know what to expect.

Main Works of Reference List (The first eight are my top favourites)

  • British National Formulary
  • British National Formulary for Children
  • Guidelines (BAD - BASHH - BHIVA - Uroweb)
  • Oxford Handbook of Genitourinary Medicine, HIV, and Sexual Health
  • Oxford Handbook of Medical Dermatology
  • Rook's Textbook of Dermatology
  • Simple Skin Surgery
  • Weedon's Skin Pathology
  • A Concise Atlas of Dermatopathology (P Mckee)
  • Andrews' Diseases of the Skin
  • Andrology (Nieschlag E FRCP, Behre M and Nieschlag S)
  • Bailey and Love's Short Practice of Surgery
  • Davidson's Essentials of Medicine
  • Davidson's Principles and Practice of Medicine
  • Fitzpatrick's Colour Atlas and Synopsis of Clinical Dermatology (Klaus Wolff FRCP and Richard Allen Johnson)
  • Fitzpatrick’s Dermatology in General Medicine
  • Ganong's Review of Medical Physiology
  • Gray's Anatomy
  • Hamilton Bailey's Demonstrations of Physical Signs in Clinical Surgery
  • Hutchison's Clinical Methods
  • Lever's Histopathology of the Skin
  • Lever's Histopathology of the Skin (Atlas and Synopsis)
  • Macleod's Clinical Examination
  • Martindale: The Complete Drug Reference
  • Oxford Handbook of Clinical Examination and Practical Skills
  • Oxford Textbook of Medicine
  • Practical Dermatopathology (R Rapini)
  • Sexually Transmitted Diseases (Holmes K et al)
  • Statistics in Clinical Practice (D Coggon FRCP)
  • Stockley's Drug Interactions
  • Treatment of Skin Disease: Comprehensive Therapeutic Strategies
  • Yen & Jaffe's Reproductive Endocrinology