Chapter XXXI: Tinea Imbricata

GENERAL CONSIDERATIONS

This form of tropical ringworm is chiefly found in the islands of the South Pacific and in the Malay Archipelago. It is also found in Southern China and quite recently has extended to Southern India and Ceylon. Recently it has been reported from Brazil.

On account of the disease having been carried from the Tokelau Group to Samoa it is often designated _tokelau_.

Manson was the first to recognize the affection as due to a fungus
which he demonstrated microscopically in the scales.

He was also able to transmit the disease by inoculation experiments and found that after about ten days a raised, brownish spot appeared at the site of inoculation. This spot increased in size until when about ¼ inch in diameter its central portion became detached, thus giving rise to several thin, rosette-like scales, free at the center but still attached peripherally. The fungus advances peripherally, leaving a smooth surface within. Again there is a similar process developing in the original central spot to again form a circle of scales within the older and more peripheral circle. The process is repeated until several rings of scales are formed each originating from the central focus as concentric ripples form on water from the fall of a pebble.

These scale circles are from ⅛ to ½ inch apart and give a festooned
appearance to the affected skin. It was formerly supposed that the
causative fungus was _Aspergillus concentricus_ but Castellani has
demonstrated that fungi of this genus, when present, are merely
accidental. He has isolated in cultures what he considers the
causative fungus, _Endodermophyton concentricum_. He treated scales
for ten minutes with absolute alcohol and then placed single scales
in a series of tubes of maltose bouillon.

The fungus grows between the rete malpighii and the external epidermal layers forming a network of mycelial threads, about 3 microns broad.

Another fungus cultured from tinea imbricata scales is
_Endodermophyton indicum._ Inoculation of this organism in pure
culture produced the disease.

The characteristics of the genus _Endodermophyton_ are: The
growth of a mycelial network between the rete malpighii and the
superficial epidermal layers; in cultures only mycelial filaments
are found; there are no conidia-bearing hyphae.

The fungus is also called _Trichophyton concentricum_.

When this skin disease is introduced into a country with high
relative humidity and fairly uniform temperature, between 80° and
90°F. it spreads with great rapidity.

A dry climate or one showing considerable variations in temperature
is not favorable for its spread.

SYMPTOMATOLOGY

The clinical characteristic of this form of ringworm is the presence of rosette-like lesions of several concentric circles of shingle-like, papery scales which are fixed peripherally and free toward the center, thus, from its imbrications, suggesting the name given it by Manson.

If one passes the finger over the affected surface from without
inward there is no sensation of roughness but if passed from the
center outward the free borders of scales cause a sensation of
roughness.

As these circles extend peripherally they meet the peripheral rings of other circles so that various curves appear which give the general appearance of watered silk.

The flaky scales are of tissue paper thinness and are of a dirty,
brownish-gray color.

The general health of the patient is not affected but the itching
is very severe.

There is an entire absence of inflammation about this ringworm thus differentiating it from the more common tropical ringworms. Again the axillae and crotch are much more rarely affected than in other ringworms as is also true of the face, palms of hands and soles of feet. The scalp is never affected.

Some claim that the fungus never invades the nails but Manson
states that this frequently occurs. The presence of the fungus in
a scale treated with 10% solution of sodium hydrate differentiates
the scales from those of ichthyosis.

Tinea intersecta is somewhat similar to tinea imbricata when
first appearing, showing dark brown patches but it never shows
the concentric rings. The ordinary ringworms present inflammatory
characteristics.

TREATMENT

A thorough preliminary scrubbing with soap and water in order better to expose the fungus to curative applications is important.

For treatment Manson recommends iodine liniment. This contains 12½% of iodine as against 7% for the tincture. The liniment has also 3½% of glycerine which is not an ingredient of the tincture. Both tincture and liniment have 5% of potassium iodide. The application of the tincture does not seem to be as satisfactory as the liniment, the stronger preparation being more effective.

Chrysarobin is very effective but very irritant and has to be
used with care. An application of a 5% solution of chrysarobin in
chloroform to the affected area, then painting it over with a 50%
aqueous solution of ichthyol, often gives good results.

Some prefer a 2% to 5% ointment of chrysarobin. Chrysarobin
produces a conjunctivitis if used near the eyes. Again if absorbed
it may act as a renal irritant.

Castellani strongly recommends the use of resorcin in tincture
of benzoin (60 to 120 grains of resorcin in 1 ounce of tincture
of benzoin). Either remedy alone has very little effect, the
combination being necessary. The application is made once or twice
daily. In addition to this treatment the patient should be scrubbed
with sand-soap and hot water twice a week.

As regards prophylaxis the clothing should be boiled. The natives
attach value in preventing the disease to anointing the body with
cocoanut oil.