Does this difference between the two forms depend on a difference in the virulence of the bacilli? This readily suggests itself. But if so, this virulence is capable of very rapid changes. We have seen a case of maculo-anæsthetic leprosy, which probably arose by inoculation from a very severe case of nodular leprosy, since the patient some years before the outbreak of the disease had for a long time shared the bed of a nodular leper. In this case the virulence of the bacilli must have been at once diminished on their inoculation on another organism. And since it also happens that a maculo-anæsthetic case may on a fresh eruption become nodular, the bacilli must be able by cultivation in the organism to re-acquire their power. Both are possible, but the virulence of the bacilli seems to depend, not so much on any constant character of their own, as on the soil in which they live.
Now it is a remarkable fact that in certain regions in Norway the nodular form predominates; in others the maculo-anæsthetic does not indeed predominate, but is present almost as frequently as the nodular. The maculo-anæsthetic cases are more numerous in the eastern districts, where the climate is dry; the nodular in the western, along the coasts where the climate is moist. And in this western division there is a region where the climate is not nearly so moist as in the division generally, and here the proportion of maculo-anæsthetic cases is distinctly higher, as may be seen by referring to [Table III], page 144.
Sogn lies in Nordre Bergenhus, and is an inland fjord with a rather dry climate. Söndfjord and Nordfjord lie nearer the coast, and have, especially the former, very damp climates.
We have already noted that the leprous nodes are most frequently found on the exposed parts of the skin, and it is quite possible that the form is determined by climatic influences.
As the Table shows, males are more affected than the opposite sex, and this too may depend on climatic influences.
It is also possible that the bacilli always possess the same virulence, and that it is solely dependant on the soil in which they live, whether they multiply freely or no. But it is impossible to say anything definite on this, so long as we are unable to cultivate the bacillus, and so long as we can only refer to the conditions in Norway; and nowhere else have we such definite statistics of the disease and its form as to justify us in drawing any conclusions.
We must, therefore, for the present leave in suspense this most important and interesting question of the virulence of the Lepra bacillus, since we possess no experimental proof of any attenuation.
Chapter VI.
DIAGNOSIS AND PROGNOSIS.
DIAGNOSIS.—In view of the description which we have given of the two forms of the disease, the diagnosis is usually accompanied by little difficulty. We have, however, noted above how a case of tubercular Leprosy, with subcutaneous nodules only, was overlooked by a doctor well acquainted with the disease; and we have occasionally seen, in the country, people described by the doctors as leprous who were not so. And, on the other hand, we ourselves were once in doubt as to the diagnosis in a tuberous case, since all the nodules were exceptionally small, and presented no characteristic appearance. But the doubt was readily dispelled by the excision of a nodule and the recognition of the bacillus. In the diagnosis of the maculo-anæsthetic cases, one is more frequently in doubt, since the maculæ have not always a characteristic appearance; sometimes they closely resemble psoriasis, and in such cases the excision and microscopical examination of a portion might clear away doubt. This we have never needed to do, since the swelling of the lymphatic glands, or a thorough investigation of the sense of touch, have always been sufficient to establish a diagnosis. Even in comparatively, recent cases there may almost always be detected some loss of sensation in the fingers and toes; sometimes it is first evident on the wrists or back of the feet. For this investigation one must either use callipers, or very slight stroking, since deeper pressure can be at once perceived. As a rule, the maculæ themselves are somewhat anæsthetic. We recollect once seeing a syphilitic eruption exactly resembling the leprous maculæ, but here the history cleared up the diagnosis.
Maculo-anæsthetic Leprosy may in its later stages be confounded with syringo-myelia, as Charcot has already noted in giving the points of distinction between the two conditions. If the maculæ are no longer present, careful investigation will often enable one to recognise their previous presence by finding areas of skin, especially on the upper arms, the back, the thighs and calves, which are somewhat paler than the surrounding skin, and in which sensation is somewhat blunted. We have thus frequently recognised the previous presence of maculæ in patients who themselves knew nothing of them. Zambaco Pasha has stated that certainly many of the cases described in France as syringo-myelia and Morvan’s disease are cases of Leprosy; that Leprosy in this form still exists in Brittany; and further, that he has there found some cases of nodular Leprosy. It is remarkable that in these last cases, where the proof would have been so easy, he has not demonstrated the Lepra bacillus. From the drawings which he gives in the Annales de Dermatol. et de Syphil. (T. III., Nr. 12), some of the cases can scarcely be regarded as Leprosy, since on the hands with mutilated fingers, no muscular atrophy can be noted; but in others there is distinct atrophy, and these may very well be leprous, the more as Pitres has published in the Gaz. des hôp. 1892, a case diagnosed as syringo-myelia in which Lepra bacilli were demonstrated in an excised portion of the ulnar nerve. It is unfortunate that Zambaco Pasha did not demonstrate the remains of previous maculæ, which would probably have been possible in some cases, were they really cases of Leprosy. According to the rich experience of Dr. Danielssen and our own, it must be admitted that a skin eruption is never absent in true cases of Leprosy. With multiple neuritis from some other cause, it is, with a good history and careful examination, not possible to confuse Leprosy; and the same is true of progressive spinal muscular atrophy, where there is no disturbance of sensation.