The early differentiation of rachitis from infantile myxcedema is very important. Myxcedematous children also present swellings on the costal cartilages and thickenings of the epiphyses of the long bones, and with them even more than in rachitis there is a delay in the appearance of the teeth, as well as in the closure of the larger fontanelle, and in learning to stand and walk. Nevertheless such a striking clinical pic ture is presented by the combination of a marked delay in the growth, with a considerable retardation of the psychic development, cretinoid physiognomy, a myxnedematous condition of the subcutaneous fatty tissue, and with macroglossia, that an experienced individual can easily make a correct diagnosis at the first glance even in the less marked cases. Furthermore in rachitis the skin is soft and delicate; in myx cedema it is dry and hard, often with much thickened epidermis, espe cially of the toes; the hair in racbitis is thin and soft, in myxtudema coarse and brittle; most rachitic children sweat a great deal, while as a rule myxcedematous ones do not; finally the poor appetite and extreme constipation of myxcedema are features which never occur in rachitis in such marked degree.
The confusion of infantile scurvy (Barlow's disease) and rachitis arises from the fact that the former malady was earlier considered to be the same as acute or hfemorrhagic rachitis. For the establishment of a correct diagnosis it should be noted that infantile scurvy preferably affects rachitic children, and that the occurrence of undoubted rachitic symptoms in no way excludes or modifies those of the other disease. Properly speaking the two diseases have only one symptom in common, namely the tenderness of the bones, and even this, especially in the legs, is apt to be of such extraordinary severity in infantile scurvy as is only very seldom seen in rachitis. The swellings on the bones in infan tile scurvy, which are caused by subperiosteal hvernatomata, are easily differentiated from the epiphyseal enlargements of rachitis by their localization, as they affect not the epiphyses themselves but the neigh boring portion of the diaphyses. There is moreover in the symptoma tology of rachitis nothing which one could at all confuse with the other symptoms of infantile scurvy, namely, the affection of the gums, and the hremorrhages into the eyelids and orbits, as well as the other indica tions of the ha‘morrhagic diathesis.
Hereditary syphilis can enter into the differential diagnosis of rachitis in manifold ways. Among others the syphilitic pseudoparalysis of Parrot is confused with it, but the localization of the bony enlarge ments differs in the two diseases. In rachitis the swelling preferably
affects the epiphyses; in syphilitic pseudoparalysis there occurs either a thick ridge which surrounds the bone just at the epiphyseal margin, or a spindle-like swelling which involves both the epiphysis and the end of the diaphysis. A further differential point is the complete flaccid pseudoparalysis which gives the disease its name, and which often re mains a prominent symptom, during the entire course of the affection. The pseudoparalysis affects the lower epiphysis of the humerus with special predilection; still this point should not be very much empha sized, as the distal epiphysis of the radius and indeed the bones of the lower extremities are often involved. More important is the fact that the syphilitic paralysis is very often unilateral or at least is more pro nounced on one side, while the epiphyseal enlargements due to rachitis are almost always completely symmetrical; and in further contrast to rachitis the pseudoparalysis affects only one joint or at most a few. Lastly the time of onset of the swelling is very important. The pseudo paralysis is a disease mostly of the first three months of life while the epiphyseal enlargement of rachitis usually occurs at a later time. In rare cases the tibial deformity due to rachitis resembles the "sabre blade" form which is characteristic of syphilis, but usually the laterally bent rachitic tibia can be differentiated at the first glance from that due to syphilis, which is laterally compressed and bent directly forward. In the rare doubtful cases the rachitic origin of the deformity is improb able if no such marked deformities are found elsewhere in the body. Furthermore it should be again emphasized that a combination of rachitis and syphilis is possible.
A marked rachitic prominence of the frontal and parietal tuber osities can so strikingly exceed the facial portion of the skull as to sug gest the occurrence of hydrocephalus, but in the latter condition the ab normal expansion affects the entire skull more symmetrically, especially the lateral areas lying below the tubera. Besides this the bulging and tension of the large fontanelle and the separation of the sutures are im portant symptoms. The position of the eyeballs in hydrocephalus is absolutely characteristic; they are rotated downward so that the lower and not the upper part of the iris is hidden beneath the eyelid and between the upper margin of the iris and the upper eyelid a strip of sclera is frequently visible.